This is probably obvious to experienced computer touchers, but going to mention it anyway, because I genuinely didn't know:

If you have a server and SSH access to it, then you can just create a Git repository on there! No need for any special software or running an additional daemon, Git can just use SSH!

You can create a Git repo on the server (assume that you're logged in as user):

$ mkdir foo && cd foo
$ git init
$ touch some-file
$ git add some-file
$ git commit -m "First commit"

And then any computer that can login to the server using SSH keys can just do:

$ git clone user@server.domain:foo

And it'll clone the repository and you can do all the Git stuff like you're used to!