X11.app is Apple Computer's implementation of the X Window System for Mac OS X. Apple's implementation of X11 is based on XFree86 and adds support for hardware accelerated 2D graphics, hardware OpenGL acceleration and integration with Aqua, the Mac OS X graphical user interface (GUI). X11.app was initially available as a downloadable public beta for Mac OS X v10.2 and later included as a standard package in Mac OS X v10.3. In Mac OS X v10.4, installation is optional by default.
The source code for X11.app is available from Apple under the Apple Public Source License.
Mac OS-only software made by Apple Computer | X servers | Compatibility layers