Mac OS X only: A lot of us are excited about Time Machine, the
new feature set to launch with Leopard that adds built-in file
versioning to OS X. However, until Leopard is released (or until
you decide it's worth the money to upgrade), freeware
application TimeDrawer provides an attractive, intuitive file
versioning system for your Mac. Every time you update a
document, TimeDrawer keeps track of your changes. You can
compare your current document to itself from as little as a few
minutes ago to much longer. It might take a little to get used
to if you've never used file versioning, and I haven't used it
for long enough to say exactly how user-friendly it is, but it
seems like it might turn out to be a great alternative to Time
Machine for people not eager to upgrade to Leopard.