A Network-Based Software KVM Switch?

ScanTron writes "This seems like such an obvious piece of software, but I can't find any implementation. Like many Slashdot users, I have a Windows PC next to my Linux PC. Rather than using a KVM switch, I have a keyboard, mouse, and monitor for each PC. I'm looking for software that would let me use only one keyboard and mouse for both machines. Ideally, moving the mouse to the edge of one PC's screen would move it onto the next, letting me send mouse and keyboard events over the network. There is no reason this couldn't be used for two Linux machines, or even a Linux machine, a Windows machine, and a Mac. Does a similar solution for mouse and keyboard sharing exist?"