Mercurial

Mercurial is a distributed source control management tool.

With it you can save snapshots of your work on documents and go back to these at all times.

Also you can easily collaborate with other people and use Mercurial to easily merge your work.

Someone changes something in text file you also worked on? No problem. If you didn't work on the same line, you can simply let Mercurial do an automatic merge and your work will be joined. (If you worked on the same line you'll naturally have to select how you want to merge these two changes).

It doesn't need a network connection for normal operation, except when you want to push your changes over the internet or pull changes of others from the web, so its commands are very fast. The time to do a commit is barely noticeable which makes atomic commits easy to do.

And if you already know subversion, the switch to Mercurial will be mostly painless.

But its most important strength is not its speed. It is that Mercurial just works. No hassle with complicated setup. No arcane commands. Almost everything I ever wanted to do with it just worked out of the box, and that's a rare and precious feature today.

I wish you much fun with Mercurial!