Synergy is a free software tool which allows you to share a common keyboard and a mouse between multiple computers on a local network (Linux, Mac, or Windows). Synergy also lets you share Clipboard contents between different systems. It’s essentially the perfect solution for someone working with multiple displays (and operating systems) on a cluttered desktop.
The only requirement is of a local network connecting all the computers together so you can define one computer as a server and the others as clients. The “server” computer has the keyboard and mouse physically connected to it. Other computers that will share the keyboard and the mouse are the “clients”.