XQuartz project (to which Apple contributes) instead.

In Mac OS X 10.4 Tiger, Apple's X11 implemented X11 protocol release 6.6 (X11R6.6). This implementation includes an XFree86 4.4 based X11 window server, Quartz rootless window manager, libraries, and basic utilities such as xterm. "Rootless" means that X window applications show up on the Quartz desktop, appearing like any other