[Kylotan]

The main difference with something like Mercurial is that everybody's checking in to their own local repositories and then sharing changes as needed, rather than everybody checking in to one place. You can check in and roll back locally without affecting anybody else. You can also be more selective about what and when you check things in, such as stopping half way through your big combat system revamp which you commit locally, making some unrelated bug fixes, and then trivially submitting a changeset of only those bug fixes to the central repository, even if they're in the same files as the ones you're changing for the combat system. Or you can easily send those bug fixes to someone else to merge into their local repository to test for compatibility with their new skills and spells etc, without needing to commit to the main source repository first. If you want a distinct 'branch', you clone a repository locally, and that's that.

I think some people might not like the idea that there isn't one single authoritative repository with clear versions and so on, but it's easy enough to designate one repository as having that role if you need. Generally I find that Mercurial just feels both simpler and more advanced than the centralised systems I've used.