Backup and synchronization

I currently use Dropbox; I will explain what it is, and what functionality I need:

Dropbox has one dedicated folder on your harddrive. Any changes you make to this folder are mirrored on a server dropbox.com provides, and if other people or computers are synchronized with that folder, the changes will also happen on their machines.

Unfortunately, DB is limited to 2 gigs of storage unless you subscribe. Is there a tool I can use to get what is, essentially, dropbox functionality, without using dropbox? I have a machine I can use for server purposes, but I don't know any software that'll do this for me.

Best-case scenario, I'll get something that I'll be able to use as my workspace when programming, so my code will be backed up automatically as soon as I save it, and synchronize so I can code at my desktop when at home and continue on the same code when at my laptop elsewhere.

>>7
Now, help me out. How would you modify that setup, to encrypt files before sending, so that it would be possible to use this with a server that you don't trust. lsyncd isn't necessary, it doesn't have to be live.

I could create an encrypted loopback device, but I'm not sure how well would rsync work with that. Sure it's incremental, but it needs to find the changes to send..

Another option would be to mount a device over network, then encrypt it locally. That should work reasonably well, but I'm not sure what to use, probably not NFS..