TimeVault
TimeVault is an application that performs a function similar to Apple's TimeMachine(TM) in their upcoming release of OSX-Leopard.
But not so glossy and 3D (yet).
It makes automated snapshots of (selected parts of) the file system. You can roll back to a previous version of a file or directory, or just view it the way it was when the snapshot was taken.
It's also integrates into Nautilus, so you can go the properties page for a snapshot'ed file (right-click in Nautilus and choose properties), and see a 'Previous Versions' tab with a calendar on it.
