Have a backup hard drive on your system to keep a copy of important files (pictures, etc.) on? The Windows File Replicator allows you to make changes to folders and files on one drive, and automatically replicates those changes to your backup drive.
Simple file replication service providing one-way replication, with a console to set up folders to replicate. Its simplicity is both its strength and weakness. It is simple to set up which is great (anybody who has used Windows DFS will appreciate this). It doesn't have the ability to copy existing folder content. A good start though and with some development could be a really useful tool.