Can I install Git server in XPennology?
Yes you can, see this article here: https://gist.github.com/walkerjeffd/374750c366605cd5123d
As far as how it compares to pure Linux, it’s much different. It’s focused on a lot of the tasks needed for a NAS and tasks you would perform, like backups, disk monitoring, and beyond. This all can be done with another linux distro but you will need to set a lot of it up yourself.
I hope this helps!