Up the Sync is a basic Google docs synchronizing program written in Java. It auto-syncs every 5 minutes by default, and can run quietly in the system tray. If the user updates a document on their computer the Google docs version is also updated.
USyncer allows to synchronize your data with server maintained by you or someone else. Includes cross-platform python server and client. Alpha version now.
Flexync (Flexible synchronization) adjusts flexibly to your synchronization needs: it is always simple in use and lightweight, runs on many platforms, on single PC or in a network of stationary/mobile agents, and allows you to use advanced options!