Mac: Beta application Tower is a graphical front-end to the popular version-control system Git. If you've never heard of Git, it's probably not for you; if you're a Git user who wouldn't mind a more GUI-friendly Git, it looks very promising.
Even if you're not a developer, you may have at least heard of GitHub, a popular host for projects using Git as their revision control. (You may have at least downloaded an application from GitHub.) Git is a lot like Subversion (which we've walked through setting up), but, for many developers, considerably better.
Tower's currently in beta, but it feels very polished. If you give it a try, let's hear how you like it in the comments.