Slack

Slack came out of failed game Glitch. They took the customised communications tool the team used to build the game and created a new stand alone product.

https://www.cnet.com/news/flickr-founder-plans-to-kill-company-e-mails-with-slack/

Pixar

Started as a hardware company. The Pixar Image Computer never sold well, but the people involved had long-held ambitions to make an animated film and eventually Toy Story saved the company.

https://en.wikipedia.org/wiki/Pixar