Synergy lets you easily share a single mouse and keyboard between multiple computers with different operating systems, each with its own display, without special hardware. It's intended for users with multiple computers on their desk since each system uses its own monitor(s).

Imagine this:  You have set your laptop up next to your desktop monitor to use both computers.  Normally, you would have to switch back and forth between the desktop keyboard and mouse to the laptop keyboard and mouse, and, if you are like me, you find yourself typing on the desktop keyboard thinking that you are on the laptop, Synergy fixes this.

Just move the mouse over to the laptop, and the keyboard goes with it.  Seamlessly.