Since nobody's mentioned Wire, it's not a 1:1 alternative but it's close in terms of chat. I don't think any 1:1 alternative to KeyBase will rise up anytime soon, hosting git and files will be a bit to build up to.
We've been using Wire in our company for a few years now, I can't say it's a great UX or bug-free, but it gets the job done and supports most things we want like being available on all platforms, key verification (proper e2ee, not like Keybase that trusts the server on first use), (group) calling and (group) video calling, audited, open source, sending files of course, timed/expiring messages, no need for a phone number upon registering... it's really quite complete if you're willing to put up with it being a sluggish web/electron client. Well, and the network effect: I wish more people were on it so that wouldn't be a barrier, but Keybase had the same issue there so this might be a good place for Keybase users to continue chatting.
Have to agree on the Wire clients being sluggish. I’ve seen this on all platforms I use (even on mobile). Otherwise it’s so nice to have something that doesn’t require a phone number and allows up to three accounts to be setup in a client for free users.
Website:
https://wire.com/en/
Their backend is open source unlike KeyBase:
https://github.com/wireapp/wire-server