Aladdin Flashback for Windows

From Phatsoft:

Get Unlimited Undos with Aladdin FlashBack�?�!

It's Simple To Use!
FlashBack allows you to recreate any document just as it was when it was saved. Every time you save a FlashBack-protected file, you create a permanent record that you can go back to any time you want. Now your ability to "undo" changes is limited only by how often you save! Save as often as you like without falling victim to "saver's remorse!"

Hey, we all make mistakes. FlashBack makes it painless to correct them.
Get FlashBack, and save your important work as often as you like without the worry of accidentally saving over something you didn't mean to. Ever have a client who never knows what they want, and then, out of the blue suddenly they do? And it was that version you showed them three months ago? Now you can give it to them, instantly. Because you've got it. Because you've got FlashBack.