Single input to multiple devices across local network?

I’ve been thinking about this for a while, but finally got around to asking the question.
Consider the situation, I have three RPis set up side by side and networked. While trying to rationalise the different setups and software I have managed to get across multiple machines, I find myself occasionally typing on the wrong keyboard or picking up the wrong mouse.
Would it be possible to have something that enables me to use one keyboard and mouse and pass the input on to whichever device might have the focus at the time. Not multi monitor support, but more multi device support.
As I move the mouse pointer from the screen/device on the left to screen/device on the right, the input focus follows.

As I move the mouse pointer from the screen/device on the left to screen/device on the right, the input focus follows.

That would be cool, especially if you have a panel of monitors. But I suspect it might require some sort of custom hardware to track mouse movements in each supported operating system and report back when the mouse has hit the top of the screen. You will need feedback from each OS concerned because of two things – not all OSs treat the mouse speed as being identical (you can configure it on RISC OS and Windows, probably Linux too though I’ve not looked) and secondly because some operating systems try to do clever things like inertia motion (where the pointer will cover greater distance if you move it quickly).

This is something that I have a particular need for, and it can all be done as driver software. I would recommend to anyone who tackles this before – if ever – I get around to giving it a whirll, that they consider implementing a port of

http://synergy-project.org/

to RISC OS, so that it can be used in conjunction with non-RISC OS machines too. Furthermore there is source code available.

Have a look at KMSwitch by Thomas Milius.