I'm looking for a sync/backup client for Windows with:
- Open source license (BSD/GPL)
- rsync deltas to a remote rsync server
- VSS support
Command line interface is preferred to a GUI.
The less of everything else, the better.
I believe that Duplicati meets all of your specifications http://code.google.com/p/duplicati/ - it supports VSS, uses deltas and has a commandline client in addition to the GUI.
I have used BackupPC before and was very pleased. My user base loved that they could restore their own files if they needed to recover data.