Teleport is exactly what I needed when I wasn’t even looking for something.
teleport lets you use a single mouse and keyboard to control several Macs. Simply reach an edge of your screen, and your mouse teleports to your nearby Mac, which also becomes controlled by your keyboard. The pasteboard can be synchronized, and you can even drag & drop files between your Macs.
With this installed on my personal MacBook (with second display) and my work-based MacBook Pro, I can easily work across all three displays as if they are one.
I haven’t tested yet, but I’ll bet I could line up several of the Macs in the house and turn my office into a war room!
(Via One Thing Well)