If you have multiple computers you need to have running and available but don’t have space for monitors, keyboards, and mouse-type-thingies (it’s an industry term, I think), you should check out Synergy.
synergy: [noun] a mutually advantageous conjunction of distinct elements
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).
Redirecting the mouse and keyboard is as simple as moving the mouse off the edge of your screen. Synergy also merges the clipboards of all the systems into one, allowing cut-and-paste between systems. Furthermore, it synchronizes screen savers so they all start and stop together and, if screen locking is enabled, only one screen requires a password to unlock them all. Learn more about how it works.
Synergy is open source and released under the GNU Public License (GPL).
I tried this tool long ago and it worked well enough that I know it works as claimed. However, I was just testing it, as I didn’t need the functionality, so I can’t really speak on how well it works for regular use. (via LifeHacker)