Free for Windows and it supports Windows 2000 and up as long as you’re running .NET 2.0. FileHamster is a great utility that runs in the background and makes backup copies of your files real-time when you save. It makes incremental copies and you can make notes on changes to each copy if you so choose. It also supports watching certain files or directories to backup and supports a multitude of plugins for compression and the like.
Definitely worth your time if you’re looking for something to keep the sanity in case you have a itchy Ctrl-S twitch.

< Mogware