Synergy

Synergy lets you easily share a single mouse and keyboard between
multiple computers with different operating systems, each with its
own display, without special hardware. It’s intended for users
with multiple computers on their desk since each system uses its
own monitor(s).

Redirecting the mouse and keyboard is as simple as moving the mouse
off the edge of your screen. Synergy also merges the clipboards of
all the systems into one, allowing cut-and-paste between systems.
Furthermore, it synchronizes screen savers so they all start and stop
together and, if screen locking is enabled, only one screen requires
a password to unlock them all. Learn more
about how it works.

Synergy is open source and released under the
GNU Public License (GPL).

System Requirements

Microsoft Windows 95, Windows 98, Windows Me (the Windows 95 family)
Microsoft Windows NT, Windows 2000, Windows XP (the Windows NT family)
Mac OS X 10.2 or higher
Unix