The coolest thing since Beryl

Have more than one computer? Check it out: you can control them both with one keyboard and mouse. Put the monitors next to each other and fire up this program. When you move the mouse to the edge of the screen, it will automatically jump to the next computer. Mac, Windows, Linux, doesn't matter. You can even copy and paste from one computer to the other. No hardware needed. I got it running in less than five minutes.  And free, of course. Really frigging cool.
Synergy

(Beryl, of course, is the thing that turns my computer desktop into a cube and gives me wobbly windows and snowflakes.)