23. Slack

Team chat

Founders: Stewart Butterfield, Eric Costello, Cal Henderson, Serguei Mourachov
Launched: 2014
Funding: $540 million
Valuation: $3.8 billion
Disrupting: email
Rival: Microsoft

Slack co-founder and CTO Cal Henderson
Source: Slack
Slack co-founder and CTO Cal Henderson

Working in teams is challenging enough. Trying to keep up with "Reply All" emails can be downright maddening. That's where Slack comes in. This San Francisco-based start-up created a messaging app for teams. Slack allows users to consolidate, organize and archive the ever-growing reams of data that modern-day work teams have to contend with.


By pulling all these disjointed electronic conversations together into a single, searchable and organized view, teams have more visibility into what everyone is doing and how — or if — they want to respond.

"Before we officially launched Slack, we built a similar tool for another project that eased our communication and made our working lives simpler ... and more productive. This ‘proto-Slack’ immensely improved how we communicated, and we realized we never wanted to work without it again." -Cal Henderson, co-founder and CTO

The company raised an additional $200 million in April, bringing its total funding to $540 million and its valuation to an eye-popping $3.8 billion. Investors include Thrive Capital, Accel Partners and Andreessen Horowitz. The company claims it has 2.7 million daily users across customers, such as NASA's Jet Propulsion Lab, LinkedIn and Spotify.

Next up for Slack: video and voice chats. Good-bye voice mail?

Disclosure: Comcast Ventures, the investment arm of Comcast, CNBC's parent company, is an investor in Slack.

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