The History Of Slack & Its Impact On Business Communication

Explore Slack's history from its beginnings as Glitch's internal communication tool to its pivotal moments, acquisitions, and its influence on competitors.

Instant messaging (IM) has evolved dramatically since Murray Turoff invented it in 1971. IM became popular with applications like Yahoo! Messenger, AOL, and MSN in people’s personal lives.

During the 2010s, platforms like Salesforce Chatter and Skype for Business (Lync until 2015 and various versions beforehand) introduced IM apps for business with additional features like team chats and video calls.

Slack was released around the same time, but nobody understood just how much of an important role it would play in the future of business communications.

IM’s focus understandably was instant communication, but Slack changed the game to persistent or asynchronous chat. And with that, work changed.

The history of Slack

The year is 2012, and Stewart Butterfield is witnessing his game, Glitch, heading toward failure.

Johnny Rodgers, Product Architect at Slack recalls Stewart’s rationale for closing down Tiny Speck. According to Johnny’s website, Stewart said:

“If we keep going as we are, we’ll burn through the rest of our money in a few months and be left with nothing to show for it. But if we stop now, we can use that money to build something else.”

As he was trying to salvage the remains of Tiny Speck (the company that made Glitch), Stewart saw potential in an internal communication tool he developed for the Tiny Speck team.

Stewart called this tool Slack, or “Searchable Log of All Communication and Knowledge”.  After Tiny Spech failed, Stewart started developing Slack to go to market as a tool in its own right.

After completing beta testing in 2013, Slack was released to the public in February 2014.

Over the next decade, Slack grew exponentially to become the fastest-growing enterprise software ever. Stewart’s knowledge of making repetitive tasks fun—thanks to his MMORPG (massively multiplayer online role-playing games) experience—played a crucial role in Slack’s success.

This infographic details what happened next in the history of Slack.

History of Slack

In January 2015, in the blink of an eye (less than a year after its public release), Slack reached 500,000 daily active users. 

But there was no slowing there. Slack doubled its daily active user count in just four months after that. And by October 2015, it had 1.7 million daily active users.

Stewart’s application was clearly a success. The time was ripe for Slack to start adding the most in-demand features.

In March 2016, Slack introduced voice calls. Just nine months later, in December 2016, Slack rolled out its video calling feature, allowing paid users to video conference with up to 15 participants.

But something happened right before Slack rolled out video calling that was to genuinely revolutionize business messaging and business communication as we knew it.

In November 2016, right before the launch of Microsoft Teams, Slack wrote an open letter to Microsoft in the New York Times, with the firing comment of “Slack is here to stay”.

Dear Microsoft letter from Slack

The battle for feature parity and market leadership that followed has proven only healthy for users of both/either Slack and Microsoft Teams. If there are message threads in Slack, there must be message threads in Teams, and so on.

Slack rolled out threaded messaging—one of its most valuable features—in January 2017. This triggered an onslaught of new Slack users, with interest from small and large businesses alike.

By April 2017, Slack had 8 million daily active users. The same month, the company raised $200 million in a funding round, valuing the company at $3.8 billion.

Just five months later, Slack raised another $250 million as part of the company’s Softbank-led Series G round. With this round, Slack’s value skyrocketed to $5 billion—a $1.2 billion increase in less than half a year.

A business this size needs a CFO, and that’s what Slack added in February 2018. The company hired one of its longest-tenured employees, Allen Shim, as its CFO.

At this point, it was clear Slack was moving towards an IPO. The real question was when. But Slack had a few things to do before it went public…

Slack’s acquisitions and build-up to direct listing

By 2018, the competition was heating up. Messaging applications, specifically asynchronous messaging, were becoming more desirable in enterprises. Terms like digital workplace became reality rather than blue-sky requirements.

Microsoft was taking an aggressive approach to move existing Skype for Business users to Teams, Cisco Jabber would become Webex Teams, and even companies like Google and Facebook (now Meta) were getting in on the scene.

As a result, Slack bought HipChat and Stride from Atlassian in July 2018. Then Slack bought Astro, an email app with smart channel functionality, in September 2018. These would be crucial to the launch and success of Slack shared channels in September 2019.

It was around this time that we saw key integrations with Gmail and Microsoft Office 365. These were vital to encourage Slack as a single place for work to get done.

While Slack’s user base was already growing at a mind-boggling pace, the acquisitions allowed the company to migrate more enterprise clients.

Prior to the launch of shared channels, in June 2019, Slack’s big moment had arrived. The company went public through a direct listing on the New York Stock Exchange (NYSE), reaching a market value of $19.5 billion.

Slack IPO

Post direct listing Slack activities

As Slack became a go-to tool for enterprise communication, something became obvious to Slack’s users, partners, and staff. Integration into other line of business apps would be crucial for continued success.

The Slack app marketplace today houses over 2,300 Slack integrations and has been a vital cog in the Slack machine. Building an ecosystem of partners whose apps can work within Slack has been a core success component.

The Slack API provides the ability for third parties to build their own workflows, apps, and middleware for Slack users to access.

While some companies mandated a single platform for business use, pockets of Slack users appeared. Programmers loved the UI and adopted this as their department-wide tool.

In-house adoption spread like wildfire, with 63% of companies using Microsoft apps using Slack in parallel in some departments.

Outside of messaging, external calling became a crucial component of the Slack experience. While Slack has no calling platform of its own (you can only make internal calls with Slack over the internet), users demanded external calling be made available in-app.

To save app and context switching every time you need to make a call, Slack started to integrate with popular communications platforms.

In 2019, Slack started allowing all users with a Zoom Phone subscription to make calls to phone numbers.

In April 2020, Slack rolled out a similar calling integration for Microsoft Teams.

Just two months later, Slack took further strides to improve intercompany collaboration, when introducing Slack Connect. The feature allows Slack users to message and share files with up to 20 organizations per channel, just like they do with internal teams.

In June 2021, following the boom of the audio drop-in app Clubhouse, Slack introduced Slack Huddles, a feature that allowed users to have unscheduled audio discussions with people in their workspace.

Slack as we know it in the modern day

July 2021 brought a turning point in Slack’s history. Salesforce acquired Slack for $27.7 billion.

Salesforce realized Slack’s potential and was ready to pay the price to bring it under the Salesforce umbrella.

“We’ve learned over the past year that the workplace isn’t snapping back to the way it was."
Bret Taylor, President and Chief Operating Officer of Salesforce.

Since the acquisition, there’s been an expected bedding period. As with any acquisition of this size, there is always likely to be a period of consolidation and upselling g of existing customers.

In June 2023, Mio launched chat interoperability for Slack and Google Chat.

Using Mio, Google Chat users can join Slack channels, exchange direct messages, and exchange files cross-platform.

Learn more about chat interop here.

In December 2022, Stewart Butterfield left the company he founded and Slack had new leadership from Lidiane Jones. Interestingly, Lidiane is former Microsoft. A sign of things to come or a pure coincidence?

Slack’s influence on business communication

Slack was released after Webex and Zoom and a few years before Microsoft Teams. But Slack led the pack with its fast growth, low churn, and excellent user interface. 

Over the course of the last decade, it’s been Slack’s slick design, ability to create custom workflows, and vast integrations that have put pressure on competitors to constantly innovate.

Stewart Butterfield had already nailed the design. But the Slack team decided to hire MetaLab to polish the interface even further.

MetaLab designed Slack a little differently than competing products by using a color scheme similar to video games.

“To get attention in a crowded market, we had to find a way to get people’s attention. Most enterprise software looks like a cheap 70’s prom suit—muted blues and grays everywhere—so, starting with the logo, we made Slack look like a confetti cannon had gone off. Electric blue, yellows, purples, and greens all over. We gave it the color scheme of a video game, not an enterprise collaboration product…vibrant colors, a curvy sans-serif typeface, friendly icons, and smiling faces and emojis everywhere.”
Andrew Wilkinson, Founder of MetaLab.

Slack gave all enterprise communication solutions a challenge—catching up with Slack’s exceptional user experience and feature set. Competitors took inspiration from Slack and observed what users liked about the Slack experience to evolve their own platforms.

For example, Microsoft Teams rolled out Teams Connect, a feature that works like shared channels on Slack, in July 2022.

Workplace by Meta added the ability to notify all group participants using @everyone in a message, just like Slack.

The list continues and the sentiment is the same. When Slack adds a feature, everyone else takes notice.

How integration and interop have been critical to Slack’s success

Most modern enterprise solutions integrate with commonly used business solutions like cloud storage and CRM systems.

Since its inception, Slack has constantly grown its integrations library to add the most popular business apps. 

Slack’s most popular apps include native integrations with global giants like Google Drive, Trello, and Zapier.

We even see integration and interoperability with what traditionalists would deem as competitors. 

Be it native or via middleware, it’s harder not to integrate with another app on Slack.

Slack’s opening up of its API to Microsoft Teams Calling, Webex Meetings, and Zoom Meetings and Phone shows an awareness that it’s not the only app for work.

Slack knew the importance of integrations from day one. And it’s helped them win more deals than not.

The future of Slack?

We’ll have to wait and see. But one thing’s for sure, integration will be at the heart of it.

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