This is closer to https://git-annex.branchable.com/
slippoint
joined 3 years ago
The closest thing to what you're describing is https://github.com/tahoe-lafs/tahoe-lafs
However they're right now in the middle of a Python 2 to Python 3 port, have to keep an eye on github for a new release.
Here's a good video on the technology: https://www.youtube.com/watch?v=8xdEyquCl2I
You can indeed self-host your own Signal server, it's just that the effort required to do so is significant and it doesn't federate. Far easier to just use XMPP/Matrix.