Synergy is a free and open source software that allows multiple computers to share a mouse and keyboard. One of the computers that the keyboard and mouse is connected to becomes a Synergy server. The other computers becomes Synergy clients. All of this is done over the network. So if your Raspberry Pi is connected to the network somehow (via Ethernet or WiFi), you can setup your Raspberry Pi as a Synergy client so you can remotely control your Raspberry Pi from another computer.

Other ways of remote controlling the Raspberry Pi are VNC and SSH. VNC requires transmitting large amounts of data because it involves transmitting screen images, thus it is slower than Synergy over a slow network. SSH is great for command line work but not for a GUI environment. Synergy requires very little data but it does mean that the Raspberry Pi needs to be connected to a computer monitor.

You can also use the Raspberry Pi as a Synergy server, but this is not recommended. One reason is that Synergy isn't perfect, certain keys or special keys do not work. Some keyboards and mice have special functions that require special drivers, which Synergy and Linux might have trouble supporting.

Although a version of Synergy compiled for ARM (Raspberry Pi uses ARMv6) is available through Raspbian's package manager, it is not the latest version of Synergy. Existing users of Synergy may have updated their server installation. The protocol changes between different versions of Synergy means that you must run the same version of the client and server. Thus, we must recompile Synergy from the source code on the Raspberry Pi.