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).
The X Window System (more commonly called X11) on Mac OS X provides significant opportunities for Mac OS X developers. Based on the open source XFree86 project, X11 for Mac OS X is compatible, fast, and fully integrated with Mac OS X. It includes the full
CocoaDialog is an OS X application that allows the use of common GUI controls such as file selectors, text input, progress bars, yes/no confirmations and more with a command-line application