Not to mention it has a great filesystem behind it with integrated git. I use it as my main document store to replace dropbox and I use it on most of my projects in place of slack.
Agreed. My friends and I who kept in touch through Hangouts (gchat or whatever it is called this week), have moved to Keybase. It works fine, although the desktop chat app occasionally crashes on macOS, and the iOS app is not optimized for anything larger than an iPhone screen.
It is VC backed, doesn't require a phone number, everything is end-to-end encrypted and has apps for all major platforms (iOS, Android, Windows/Mac).