Slack… love it hate it, its seems to be going everywhere…
We recently had to move slacks for reasons not worth mentioning. I was pretty impressed as one of the founders of the data portability group way back, how easy it was to export one slack into another slack. If only more services would take note!
Flickr was famously developed as a side feature for the MMO Game Neverendingthat Butterfield was developing with his then-wife Caterina Fake and the rest of their company, Ludicorp. The team realized that the photo-sharing aspect of the game could be spun off into its own service.
Always reminds me of sitting in the audience at the doors of perception 6 in Amsterdam when Stuwart Butterfield talked about the concept and plans.