Dads Question of the Week

We've all heard the comment "that _________ is the best thing since sliced bread." In your opinion, and excluding sliced bread, what invention do you feel has contributed the most to man's arsenal of tools? Is it the Garden Weasel? The flathead screwdriver? The  hammer drill?

And since this is a dads website, feel free to throw in any experiences you've had teaching your kids how to use different tools.