Slack started out as an internal chat tool by Flickr co-founder Stewart Butterfield's Tiny Speck, which was trying to launch the game Glitch. When Glitch failed

Slack started out as an internal chat tool by Flickr co-founder Stewart Butterfield's Tiny Speck, which was trying to launch the game Glitch. When Glitch failed, they spun out Slack as a new company (or they renamed the company, not sure). This is almost the exact thing that happened with Butterfield's first venture, Flickr, which was built on a web platform they wrote for a multiplayer online game called Game Neverending (which is why Flickr URLs have/had "gne" in their URLs).