Free XQuartz Alternatives
XQuartz is described as 'The XQuartz project is an open-source effort to develop a version of the X.org X Window System that runs on Mac OS X'. There are three alternatives to XQuartz for various platforms. The best alternative is Wayland, which is both free and Open Source. Other great apps like XQuartz are X11 (Free, Open Source) and Mir (Free, Open Source).