iFolder - I just came across this. Open Source from Novell that builds functionality similar to Dropbox. Only that you operate your own server (a Linux box, ready-made packages for Open Suse). The whole thing is built with Mono, clients for Linux, Windows and Mac. I haven't tried it yet (Dropbox works too well for me to feel a great urge for changes), but I think before the next renewal with Dropbox I could take a look at it. Hosting a Suse box somewhere (or getting the server to run on Ubuntu or Debian) shouldn't be the biggest problem and I'm already hitting the limits of the 50G option from Dropbox. What I haven't found is access to older versions of files - but I haven't looked through the quite extensive manuals yet.