I’m using Dropbox for many things, and it works pretty wonders for shared collaboration if you have a small team. Especially good for artists + coders combination since others can instantly run the stuff coders do, and artists have nice way to put their stuff. (Of course keep in mind that no 3rd party system cannot be relied on, you must have your own backups and you must think twice for which purposes you want to use it)
It works on several platforms (Windows, Mac, Linux, and Mobile)
And it works when offline.
And it’s free: 2GB free space right away.
And one gets more free space when you invite other folks, so… get Dropbox (and help get me precious +250 MB more free space if you join through this link and install it on your machine, which would be greatly appreciated thanks you very much)
P.S. In fact, if you join through my link, you might get extra +250MB space as well. (At least one guy just reported receiving this). Pretty sweet!