That's unfortunate. I assume Zoom would have no interest in open sourcing the server software now that they've paid for the cryptographic expertise and code, but I think the previous owners might have been willing to... surprised they never did, maybe they decided they'd never get bought if they did.
A shame, it seemed to work really well. Maybe Zoom will be willing to take my money to be a DropBox end-to-end encrypted cloud sync service instead, they seem to be fairly on the ball with responding to complaints and that they decided it was worth buying Keybase to improve their service maybe they'll come out alright.
Wishful thinking maybe =)
Not exactly. The clients are open source, but the central server isn't. See https://github.com/keybase/client/issues/6374. It might be possible to reverse engineer the server, but it would be a lot more involved than just forking the project.