An implementation of the X Window System that makes it possible to run X11-based applications in Mac OS X. Based on the open source XFree86 project — the most common implementation of X11 — X11 for Mac OS X is compatible, fast, and fully integrated with Mac OS X. It includes the full X11R6.6 technology including an X11 window server, Quartz window manager, libraries, and basic utilities such as xterm.