Synergy, from Symless, lets one keyboard and mouse control several computers over your network. Move the pointer off the edge of one screen and it moves onto the next computer. Macs and Windows PCs can share the same set.
Symless currently offers classic Synergy and a new alpha called Synergy Dragon.
The computers form one Dragon network. One computer leads, the rest join it, and new builds install themselves. It is still alpha software, so expect changes between builds.
One computer runs as the server with the keyboard and mouse. The others connect to it as clients by its network address.