My current setup consists of several "client" computers that I have to manually back up to one linux "server" computer, which I then copy to an external hard drive(the "clients" and "server" are all normal computers, but I back up new files from the "client" computers to the "server" computer, not the other direction). I am looking for a backup solution that is free, works on Windows, Ubuntu and Mac OS X, and backs up the files in a way that they can be used (so the data is stored like a normal file in a folder on the server computer, not like some encrypted folder.) I tried CrashPlan already, but as far as I can tell, backups can't be used on another computer, and backup folders can't be merged. (so if the client computers all backed up on one server comp, there would be 5 locked folders and too much redundancy).
I think that what I'm looking for might tend towards file syncing rather than auto back ups, but I'm not sure.
Well, I have a similar set up and have been using Windows Live Mesh. Microsoft just announced they are discontinuing the service so I'm looking for an alternative.
I understand that you came here for a definitive answer. Unfortunately I'm one of those people who is in the middle. I know enough about computers to "fix" my own but not enough to offer an immediate, definitive answer.
Something I spotted on Lifehacker.com is a program called FreeNAS. You may want to search their site and read some of their articles. Even if FreeNAS isn't the solution for you their articles may refer to other programs that might provide you with a solution. Or maybe the concepts they talk about will spark something for you.
You may also want to look on Lifehacker at their articles on using Dropbox (and other services) for file syncing. Depending on the amount of files you need to sync the "free" space may be enough to get them from one computer to another. They you could manually copy them out of the "free" sync'd folder into a folder on your server. (Hmm, I wonder if you can put a shortcut into Dropbox? Would that then copy the files directly to a "real" directory?)
I use Carbonite (or any online backup) to back up my "server." That might offer some addition features that may help provide you with a solution.
If I spot something else while I'm searching for a way to sync my files I'll come back and post it.