Input Director is a Windows application that lets you control multiple Windows systems using the keyboard/mouse attached to one computer. It is designed for folks who have two (or more) computers set up at home and find themselves regularly sliding from one system to the other.
HotkeyNet is free multiboxing software. It's a hotkey program for gamers who play several characters at the same time. It lets you control several programs on your network from any keyboard no matter which PCs the programs are running on.