Can I use X Window System applications on Mac OS X?
Yes. There are several X Window System servers for Mac OS X. All are full implementations of the X Window System, and are based on Xfree86, which has fully supported Darwin/Mac OS X since release 4.0.2. One is the free Apple X11 for Mac OS X, another is XDarwin, and another example is Tenon Intersystems’ commercial Xtools.