Synergy - Cross-platform software for sharing your mouse and keyboard between multiple computers
DisplayFusion - DisplayFusion will make your multi-monitor life much easier.
Input Director - Control multiple windows systems with one keyboard/mouse. Share a keyboard and mouse across multiple windows system.
WindowGrid - Quickly and easily layout windows on a dynamic grid using just the mouse.
Barrier - Barrier is a cross-platform software for sharing your mouse and keyboard between multiple computers...
Mizage Divvy - Divvy is an entirely new way of managing your workspace.