I'm on a Mac and I had purchased a program called Downsize like 8 years ago for 6 dolla. They have a permanent file on me in the event I lose my program like when I upgrade or get another Mac and will give me my purchase number I also get free upgrades.
I love this program because it's almost too easy to use.
Stunt Software - Downsize
(edit) WOAH. They raised their prices. But man I use this all the time.