It's called Darik's Boot and Nuke. Okay, maybe some (or all) of you have heard of it, but I just found out about it.
You load it onto a boot disk, boot from it, and it overwrites your data I believe 35 times (in accordance with
Peter Guttmann's research. As in, your hard drive is bare and the data is non-recoverable. It's nuked.
Okay, I can see some uses that support illegal activity or are tampering with evidence (clearing your computer if you're a pedo, cracker, or are being sued by the RIAA or some such). However, you can have all sorts of fun. Like telling my brother that if he starts snooping on my computer one more time my hand may just accidentally knock the disk into his floppy drive, brush the power button, and hit a key when it asks if it should boot from floppy...
(it ain't the content, it's the principle of the thing. Okay, and the content)