Synergy is a tiny little program that allows you to share a mouse and keyboard between two networked computers. Right now, I have the Synergy server running on my Windows 2000 work machine and the prettied-up Synergy client for Mac OS running on my iBook. I can now literally run the mouse off the left side of the Windows machine and it appears on the iBook. It even lets you copy and paste text back and forth. Toooo Coooool.
If you're running two computers at once, this appears to be an indispensable utility.
Found at LifeHacker.