TimeDrawer looks like a very interesting document versioning utility that gives you a preview of Leopard's forthcoming Time Machine functionality. It installs as a system preference and "stores your files everytime you update them." It allows you to go back and visually ascertain the differences in previous versions with an Expose-like modal interface (though obviously a far cry from Time Machine's groovy out-of-this-world thing). You activate the interface with a contextual menu, so you can see changes in files on your desktop or within a given folder, etc.
There have been some previous document versioning applications like Versomatic, but TimeDrawer's interface looks very slick. On the other hand, it's hard to imagine TimeDrawer will last long once Leopard is released (except maybe for those who stick with Tiger, which it requires). On the positive side, TimeDrawer does not require an external drive like Time Machine.
TimeDrawer is now in beta and is a free download from ONERIVER software