I know we have quite a few customers who use their Mac minis as subversion servers. The number has increased since Leopard now ships with Subversion 1.4.4 and Apache2 pre-installed. (Of course, you’d need to configure the server. But there are good instructions here and here.)
Versions is a client for a subversion server. It was recently released as a free beta and offers a nice new way of interacting with the Subversion server.
So, if you’re looking for a nice way to keep versions of your work. Or, if you work with a group and want to make sure everyone is working on the most up to date work, then you can download Versions here.