[asdkhadsj]

You can define local path or remote git repos as dependencies if you like. That does involve Cargo of course, but if you choose it should theoretically not leave your firewall.

Also, you can run a local copy of all the documentation in all the repos pretty easily too.

Huge asterisk: I've never tested any phone-homes, if that is what you're worried about. But, it can be pretty offline-friendly.