Synergy is a software that allows you to share a mouse and keyboard between multiple computers. Friends who are juggling multiple mice and keyboards due to having many computers will find this tool very helpful. This software enables the function of operating multiple screens simultaneously. Apart from windows not being able to span across screens, the clipboard, mouse, and keyboard can all be shared effectively. Moreover, this software supports Linux, Windows, and Mac.
More importantly, this software is open-source.
Website: synergy
Download: Download Synergy and its source code here