Synergy vs. Synergy
So, their’s Synergy:
a tiny Cocoa application for Mac OS X 10.2 (and later) that puts three buttons to control iTunes in your menubar
There’s also Synergy:
easily share a single mouse and keyboard between multiple computers with different operating systems, each with its own display, without special hardware.
Normally, I’d suggest a Googlefight, but that just doesn’t seem practial.