Once in a while you discover a piece of software and wonder how you could have done without for so long. Such a tool is Synergy. If you have 2 or more computers sitting next to one another forcing you to either use multiple keyboards or even a KVM switch to navigate through the screens, you owe it to yourself to look at Synergy.

This is an open source client/server application that allows you to control any computer mouse and keyboard from any other computer. Those don't have to have the same O/S and so you could easily have a macbook, a PC and a Linux box controlled by the same keyboard and mouse attached to either one of those computers.

You need to install the software on all the boxes you need to link. The one that has the keyboard and mouse is called the server. The others are called clients. You then need to specify how the screens are laid out (in other words which machine is on the right and which one is on the left). To switch control from one computer to the next you then just move the mouse over to the screen of that computer and you can now control the other machine. Completely seamless.

And as added bonus, you can even share the clipboard from one machine to the next. That, no KVM switch will do! Just copy and paste as if you were on the same machine. While cross-OS copy and paste only supports text, this is still very useful.

There are 2 caveats. The first one is that installation is really counter-intuitive. That's the most painful part of the process. But fortunately there is a very good walk-thorough at Lifehacker. The second one is due to a limitation in Windows: the inability to transfer the Ctrl+Alt+Del key combo to another client machine. Fortunately there is a workaround: if you install the client as a service (and don't forget to restart your computer after that), you can then press Ctrl+Alt+Pause to emulate the Ctrl+Alt+Del combo.

This application is not new and the code has not been updated since 2006 but this small piece of open-source software is a must-have for whoever needs to use multiple computers at the same times on a regular basis.

UPDATE: a new fork has been released that fixes some of the bugs from the original version. It's called Synergy+ and this is the one you should use.