The X Window System (more commonly called X11) on Mac OS X provides significant opportunities for Mac OS X developers. Based on the open source XFree86 project, 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. Whether a Unix user or an X11 developer (or both), Mac OS X offers a platform where your applications can run without modification. On a Mac, any of the thousands of available X11 applications can run in a window running concurrently alongside iTunes, Microsoft Excel, and any other Cocoa, Carbon, or Java applications.
There are some things to know about X11 on Mac OS X before you start, and this article outlines the key issues you should be aware of. Many existing X11 applications from the UNIX world are available to use for free—if you know the "secret handshake." That is, you can often easily get the source code, but it's up to you to build and install the product. There are some binary distributions available as well, with applications pre-built for X11 on Mac OS X. This represents a new source of useful software that you don't want to overlook.
We first review some X11 basics (for those new to X11), then discuss installing the X11 environment on Mac OS X and starting it for the first time. This section includes a description of the advantages stemming from integration with both the Finder and Quartz. It also discusses differences between Terminal and xterm, and full screen support. Next, several X11 configuration issues are covered, including X11 forwarding, configuring xauth, using ssh to run remote sessions, and PseudoColor support. Then come examples of building X11 applications from source using configure, IMake and xmkmf; and installing binaries using Fink. We conclude with instructions on downloading and running OpenOffice, and point you to further resources for next steps.
This article details pretty much everything you need to know about running X Windows on top of Mac OS X.