Slack case study: the fastest-growing business app in history (Part 2)

Updated on October 18, 2026: data reviewed and updated.

Slack case study: the fastest-growing business app in history

Chapter 5: An offer you can’t refuse

Once a product breaks into a market with high potential, the speed of its growth depends on whether it can keep lighting the fuse that sets off the next explosion.

Whether a product can go viral depends on factors such as:

• Your product becomes part of users’ daily or regular routine
• It is easy to share and to pull more people onto the platform
• Slack has an excellent freemium option and reasonable pricing.

Right from the start, you can use all of the features Slack makes available, such as integrations and document sharing, and you can take advantage of the rest of its built-in tools as well.

The limits of the free account do not get in the way when people first start using it. Upgrading only starts to make sense once Slack has become an indispensable part of their workflow. By that point, Slack has already hooked you.

The limits of the free plan (according to Slack’s pricing page in 2026):

• You can only view and search message history from the last 90 days
• Data older than one year is deleted
• You can connect a maximum of 10 apps

All of this is done on purpose. Slack wants you to keep using its product until you realize that communication has become easier and the tool has turned into a daily part of your working life. Then, when you reach the point where you want more storage or more integrations, you upgrade to the paid model. By then, the product is already built into your workflow and your day.

Slack is an exception when you look at this conversion percentage. In the freemium model, the conversion rate from free to paid is usually only a few percent.

Spotify is a standout case: in June 2015, the company announced it had 20 million paying subscribers and 75 million active users (What Hi-Fi, 6/2015).

One important point is that Slack is a tool for connecting teams. As soon as you open the desktop app, you are prompted to invite your team members. Inviting teammates is one of the steps in the onboarding journey.

Even inside the app, the call to action is highlighted in several different ways:

• Slack asks you to invite your team members right away.
• Slack makes it easy to share an invitation link.
• You can invite users through a unique URL that can be shared by email, on social media or on any website.

Shifting the definition of success from activation to referral

Slack was built around the concept of a product that people love. And when people love something, they will tell their friends and their colleagues all about it.

CMO Bill Macaitis successfully shifted the focus from converting users to paid accounts toward persuading users to recommend Slack. That seems like a hard thing to achieve. Paid conversion is only a short-term goal; it plays an important role, but it is far less significant than achieving a large network effect.

A network effect is the condition in which each new user who joins makes the product more attractive to everyone else. Each person who uses Slack becomes more likely to win over their whole company to Slack. That explains why the emphasis on NPS (Net Promoter Score) and CSAT (Customer Satisfaction) as the key metrics brought the biggest success. It is the ideal way to optimize for word-of-mouth marketing.

And the perfect example of this is Slack’s pricing model.

If a member of a paid workspace does not use Slack for more than 28 days, Slack automatically adds a credit for the unused time to the account, a policy that is rare among software companies.

Let’s think about frictionless testing. Slack had to ask itself what was best for both its brand and its customers:

• Does the pricing model fit a customer-centric approach?
• Does the model surprise users in a positive way? (Yes, because the workspace is credited for the fees of inactive members.)
• Are customers likely to recommend the product? (Unusual things tend to get shared more.)

Going deeper into customer success

In the book “From Impossible to Inevitable,” Aaron Ross wrote that customer success is the core driver of growth and is worth more than 5 times as much as sales.

That is also the reason why Macaitis, who came from Zendesk, where he had focused on CSAT scores, treated customer success as the number one priority.

In The Power of Habit, author Charles Duhigg explains the concept of keystone habits, “a personal pattern that can unintentionally set off other habits in a person’s life.” These are the beliefs and habits that someone, or in this case a company, values most.

Just as sticking to a daily exercise schedule helps individuals become more organized, gain more energy and start eating better, customer success has a direct effect on retention, generates referrals and helps you collect positive case studies.

The lesson to take away here is to give away so much value that your users simply cannot live without you. Create a product and an experience good enough that they want to tell all their friends about you. Make it easy for people to start using the product and to bring their friends and colleagues onto it. Competitors can copy the basic features, but they cannot copy the community.

Chapter 6: The formula for building a billion-dollar company

Having a great product is not a ticket to getting rich. It is only the precondition for growth. But there are two ways you can grow. There is the slow, hard way, where it feels like you are pushing a boulder up a hill. Or there is the easy way, where it feels like you are steering a wheelchair down a slope.

And of course, there are also huge products that achieve astonishing growth. Brian Balfour, the former VP of Growth at HubSpot, explains that you need 4 pieces of the puzzle to grow to $100 million in ARR:

• Market/Product Fit
• Product/Channel Fit
• Channel/Model Fit
• Model/Market Fit

The companies that can line up these 4 frameworks and apply them correctly are the ones whose growth seems to happen naturally.

• Market/Product Fit

Building a great product is necessary, but you still need to find a market. Find the problem before you build the fix. We should think about the market first, and the product after that.

For example, in 2016 and 2017 there was a great deal of hype around VR. VR sounded new and exciting, and many startups and other companies tried to build something or other around it.

Or take the last few years, when cryptocurrency and blockchain showed up in every online magazine. Yet there is still no clear, tangible use case in which those technologies are fixing a real problem.

That is because they do not solve any big pain point.

Slack’s team communication has a very clear value proposition: cut the time and effort spent on team communication so people can get the information they need right when they need it. As a result, work runs more smoothly and more productively.

Take a look at the information below:

Market/product fit has to be proven with a combination of qualitative and quantitative measures.

Slack’s North Star metric has always been NPS, one of the best qualitative predictors there is. If your product solves a problem and is built in a way people love to use, they should be recommending it to others.

At the same time, on the quantitative side, you need to pay attention to two things: direct traffic and a retention rate that holds steady.

Slack figured out both. The product is like quicksand: the more you use it, the more you depend on it. Even people who join the company later have to use it.

• Product/Channel Fit

What most startups fail to understand is that the product and the channel are connected to each other. We should not treat them as separate boxes holding the things you need to do. They are not separate entities but connected pieces that correspond to each other.

Products are built to take advantage of specific channels. But the channels do not shape themselves around your product.

We cannot set the rules of the channels. Google decides what ranks in SEO and what is shown as a search result. Facebook decides what appears in the News Feed. Gmail decides what goes into the spam folder and what goes into the promotions tab.

What you need to do is fit your product into one of these channels as smoothly as possible.

And that is what Slack did.

Slack’s product has an incredibly fast time to value, and it targets not just an individual but a whole team.

Second, Slack has a broad value proposition: everyone on the team gets the same benefit of higher productivity and less time spent waiting for information.

Even so, Slack found a way to push all of that into the one channel with the strongest impact: word of mouth.

Peter Thiel, one of the best-known venture capitalists in Silicon Valley and a co-founder of PayPal, said: “We don’t live in a normal world; we live under a power law.”

The power law of distribution tells us that 70% or more of all acquisitions will come from one source (or one marketing channel).

Slack’s traffic tells you what its source is:

It is not just virality but a combination of brand and word of mouth. It is the “direct” channel. This means the Slack brand is so well known that most users reach the website by typing slack.com straight into the browser. Every company dreams of having this kind of distribution channel.

You have probably heard of the Pareto principle (also known as the “80/20 rule”): 20% of your effort produces 80% of your results. The power law of distribution is similar, and it is what Peter Thiel was referring to in his quote: “We don’t live in a normal world; we live under a power law.”

This is explained by Product/Channel Fit. Every business uses one or more channels to acquire users or revenue. In the book Traction by Gabriel Weinberg and Justin Mares, you will find 19 marketing channels you can explore.

But it is simply not normal to expect your traffic or your users to be spread evenly across different channels. Truly successful companies find one channel that brings in 70% or more of their users.

Some examples of companies that have done this:

• Virality: Dropbox’s storage referral program and Harry’s razor waiting list
• SEO: HubSpot and Neil Patel, who has a firm grip on almost every area of marketing through content
• User-generated content (UGC): Reddit, TripAdvisor, Twitter, Instagram
• Sponsored podcasts: the website builder Squarespace and Casper are known for sponsoring podcast hosts who plug their products.
• Channel/Model Fit

Channel/Model Fit defines the relationship between your pricing model and your channel. It answers the question of how you charge your customers and what average annual revenue per user (AARPU) you are earning. Put another way, ARPU (Average Revenue Per User) is “a measure of the revenue generated per user or per unit.”

To identify a good business, we need to look at the relationship between ARPU and customer acquisition cost (CAC):

At one end, you have low ARPU and low CAC. These are channels that make money fast. Think of Facebook or Mailchimp.

At the other end, you have high ARPU and high CAC. These are companies like Palantir Technologies.

A company’s pricing model has to be a good match for its channel. According to Brian Balfour, the worst place to be is somewhere in the middle. That does not mean it cannot work, but it can be harder to execute.

So what about product tiers, which let you offer your product at different price points with different features? Here is an example of product tiering from Mailchimp:

Larger products with many different features can exist at several points along the ARPU <> CAC spectrum. If you look at LinkedIn, it has product offers at both the low end and the high end.

Where does Slack fit?

We have defined Slack as a product that uses virality to grow. The freemium model lets a whole team join and lock in the value it gets very quickly. But most users convert to the paid version within the first three months. That puts Slack just to the left of the middle of the spectrum.

At the product level, Slack has benefited from transparent pricing. But it also has a solution at the higher end of the spectrum: Slack Enterprise Grid. With Enterprise Grid, companies manage multiple workspaces with enhanced security features.

Model/Market Fit

For some companies, growth can feel like a woolly mammoth, where you have to put in an enormous amount of effort just to grow. For others, growth is a natural process that runs smoothly; it feels as if growth just happens on its own. Slack is clearly one of the latter.

Why is that? Because the road to $100 million in annual revenue is different depending on your pricing model and your market. Christoph Janz of Point Nine Capital developed a pricing matrix and named the different products after the animals they represent:

• Elephant: large enterprise customers paying $100,000 or more per year; you need 10 customers to reach your first $1 million in revenue.
• Deer: mid-sized businesses paying about $10,000 per year; you need 100 customers to reach your first $1 million.
• Rabbit: small businesses paying about $50 to $100 per month, or roughly $1,000 per year. Most SaaS software for small businesses falls into this group.
• Mice: individual users paying about $100 per year.
• Fly: each user brings in about $10 per year, usually through advertising.

Where your product sits in the Animal Pricing Matrix decides your market. Are you going to hunt big corporate and enterprise deals? Or do you only need a few of them?

Slack’s default product is the rabbit: small teams (2 to 20 people) up to mid-sized teams (up to 150), from whom it can quickly earn a decent amount of revenue. Because it earns per user, the price can climb quite quickly. For that reason, Slack held the record of adding one million dollars in ARR (annual recurring revenue) every 11 days. That is especially impressive because it happened in the first year after launch.

If you draw a horizontal line across the “animals,” you get the Model Market Fit Threshold: everything on and to the right of the line meets the Model Market Fit Threshold, while everything to the left does not.

Here is how you calculate your own Model Market Fit Threshold:

Start with the total number of customers in the market, which you already worked out at the Product Fit stage. If the customer base feels too small, you can widen it. However, you need to check your Market Product Fit to make sure you are still covering customers who meet your criteria.

Next, calculate how much your customers are willing to pay. You need to be above the Model Market Fit Threshold. If your product falls below it, you can raise your prices, but make sure your Product Model Fit still supports a positive ROI.

Finally, think about what percentage of the market you can realistically capture. This is the hardest number of all to calculate, because it is so difficult to predict. Brian Balfour suggests 10% as a rule of thumb and a starting point.

Applying all 4 frameworks to Slack

Let’s put Slack into the analysis below, using its valuation of $5.1 billion in 2017 (in 2021, Salesforce acquired Slack for $27.7 billion).

Over the years Slack has grown to cover a larger share of the market with different pricing models, but for the sake of this equation, let’s look at the most common one:

• Product: Slack is a team communication tool that solves the problem of internal communication inside a company. It has a clear value proposition and solves a real pain point. Slack is simple to use, and with a huge number of apps and integrations it becomes a valuable part of a company’s systems.
• Market: its most common customers are software companies that start with a small headcount (5 to 20 employees) and often grow quickly to hundreds of people or more.
• Model: Slack charges by the number of active users. A 20-person company on the Pro plan, billed annually ($7.25 per person per month), pays about $1,740 per year; each new member adds about $87 in revenue per year. That puts them at a mid-range ARR.
• Channel: word of mouth, accelerated by high customer satisfaction scores. Each user who joins Slack is also likely to draw others in. Because the product is simple and needs little setup, the viral channel works remarkably well.

There are about 20 thousand tech startups in the Bay Area. Since 10% of 20,000 is 2,000, that means 2,000 companies with 20 users each, producing an Annual Contract Value (ACV) of $4 million.

But Slack does not only target software companies; it also serves ordinary traditional shops, offices and government agencies. As mentioned earlier, the TAM is enormous.

Slack expanded its model with an enterprise option, where it no longer hunts rabbits and mice but goes after bigger animals. Virality and word of mouth are the most scalable channels it could ask for. Slack identified users’ pain points and wishes, and that gave it the momentum to reach new international markets. In fact, more than half of Slack’s users are in over 100 countries outside the United States.

These markets are served with localized support and services. Every channel keeps evolving and keeps running, which demands that every company keeps working at and managing all 4 frameworks.

Chapter 7: Slack’s relationships: partnership moves and integrations

Successful companies often buy another company to get rid of competition (TripAdvisor bought a large number of local travel apps), to gain a wider customer base (Amazon with Whole Foods and Zappos) or to get access to proprietary technology that will help them grow (Facebook with Instagram).

Most big companies wait for the disruptor to reach a certain stage of development before they move. The acquirer removes the threat, stops other rivals from moving in and taking the technology, and gains immediate access to a new audience. Sometimes an acquisition happens simply because a company needs senior development talent and knows that a young startup has some of the best minds in the business.

Mergers are another strategy. When Facebook bought Instagram for about $1 billion in 2012, many people thought the price was far too high for a photo app with only 13 employees and no revenue model.

But 6 years after the merger, Instagram had one billion monthly active users, all of them exposed to Facebook Ads campaigns. At the end of 2017, eMarketer forecast that Instagram’s ad revenue would grow from $4.10 billion in 2017 to $10.87 billion in 2019 (The Drum, 12/2017).

Slack’s product idea is not hard to replicate. Internal chat technology is not very different from Internet Relay Chat (IRC). Remember that Campfire, Yammer and HipChat had been solving the team communication problem for several years before Slack launched. But for Slack to stay ahead, it had to grow fast. As Matthew Lynley of TechCrunch once put it:

“Companies like Yammer, Microsoft and others have sought to remake internal communications in ways that look more like consumer tools in the Web 2.0 era, but Slack took an approach that started out as just a chat and team communication tool.”

Naturally there were other competitors, so Slack decided to use M&A to strategically fill the gaps in its success:

• September 26, 2014: Slack acquired Spaces. Spaces had document collaboration technology that significantly expanded what Slack could do.
• January 28, 2015: Slack acquired Screenhero. The messaging app had no screen sharing or voice chat at the time. All six employees who had worked for Screenhero joined Slack.

• July 17, 2018: Slack acquired Missions. Missions, an app from Robots and Pencils, let Slack users build tools that automate simple processes without much technical knowledge. The tools are very much like Zapier for Slack users. Integrations are central to Slack’s success: by 2026, Slack had more than 2,600 apps in its App Directory.

According to TechCrunch, 94% of paying business users use apps and integrations, while 65% of teams have built their own. With Missions’ visual builder, creating new integrations is easy and allows the customization Slack users want.

• July 27, 2018: partnership with Atlassian. Slack announced it was acquiring the Stride and HipChat products from Atlassian. Slack and Atlassian already had a relationship: Atlassian tools such as Trello, Bitbucket and Jira were already integrated with Slack, adding project management to an already strong communication tool.

Acquiring Stride and HipChat let Slack upgrade its product’s workflow capabilities, especially for large enterprises. The Stride collaboration tool allowed video, voice and chat at the same time, while HipChat was one of Slack’s biggest competitors. As the first mover (HipChat launched in 2010), it had built up a substantial user base over many years before losing out to Slack’s rapid user growth.

Both HipChat and Stride were to move their users over to their former rival’s platform and end support in February 2019.

The lesson here is that an acquisition does more than remove competition. Think about what else you could gain by buying a competitor or a free product: a customer base, new talent, new technology?

Chapter 8: Future-proofing the company and the product

We have seen many high-growth companies “rest on their laurels” instead of continuing to iterate and optimize.

How did Slack protect itself against the big players? Before it was taken over by Salesforce in 2021, Slack had to compete with Microsoft Teams and Google Chat (formerly Hangouts Chat), two rivals with huge distribution advantages.

From the beginning, Slack’s intention was to build a solid, customer-centric product that was not only functional but also genuinely loved. Much of its marketing effort went into making the brand fun, pleasant and approachable. People who use Slack share the same perception of the brand, and Slack has lodged itself in users’ minds because it put so much effort into getting its core message across.

This is something that neither Google nor Microsoft could achieve. Not in the short term, at least.

They may be able to offer the best integrations, tools and technical polish, but it would still be a Google or Microsoft product: a product from a big company that owns everything.

When someone looks at Slack, they see the Animal! videos with bright colors and an unusual message. When they look at Microsoft, they see a different brand message: a more corporate machine with a serious tone.

That is also why HipChat, arguably the same product and launched 4 years before Slack, could not grow.

Slack won the branding game because it invested in its Wall of Love.

Integrations and technical flexibility keep the team ahead in the team communication industry. The strategy of acquiring companies let it bring in the best talent and an instant increase in new users.

Stewart Butterfield talks about the importance of inclusion and diversity, and it is not just an empty signal. According to Slack’s 2018 diversity report (HR Dive, 4/2018):

• 48.1% of management positions worldwide were held by women, up from 43% in 2017
• 11.5% of staff came from underrepresented racial and ethnic groups
• 7.8% of staff identified as LGBTQ
• 1.7% of staff were people with disabilities

This is significantly better than companies such as Google, Facebook or Microsoft, where women hold 19% to 28% of leadership positions and 19% to 20% of technical roles.

It tells the public that Slack cares about its employees. And because it cares and provides an inclusive and safe environment, its Glassdoor reviews speak very highly of it:

Finally, the core Slack team, the original founders, really enjoy working together. They went through hard times together, through sprints and through the failure of earlier products that did not work out. They are bound together by a shared goal of keeping customers happy.

If you look at military history, battle-hardened soldiers from the same company perform far better than new recruits. Every individual in a close-knit unit knows the others and cooperates with them, because they know exactly what each person is capable of.

In his book From Impossible to Inevitable, author Aaron Ross talks about deciding your own fate: at every moment of building a business, you have two choices:

• You give up when you face a challenge
• You use the challenge to push yourself and others forward

In BUD/S (Basic Underwater Demolition/SEAL), a notoriously tough phase of training to become a SEAL, the training officers worked out who would make it through. It was the individuals who found a friend, a brother they could trust and work with under the most mentally and physically exhausting conditions. As Stewart Butterfield said in a “How I Built This” interview with Guy Raz:

“You go through a psychologically difficult thing with a group of people, and you really bond with them. So I think we all wanted to keep working together.”

The lesson here is that your brand is everything your company does for its customers. Tie everything back to that mantra: employee happiness, love for the product and, most important of all, customer satisfaction.

Conclusion of the Slack case study

Slack has established itself as the idol of business software companies. It is loved by small startup teams and by large enterprises alike. Slack’s solution for internal communication is not only effective; it is also delivered in a way that is easy and fun to use. Its intense focus on customer satisfaction has only made Slack better for new users over the years. And above all, its employees enjoy working there and believe they are making a positive change. In July 2021, Salesforce completed its acquisition of Slack for $27.7 billion.

This article was adapted by Adtek from original Single Grain content (2019), updated on October 18, 2026.