Penguin
Recent Changes

For 10.2 and higher, Apple have a free X11 server available for download from http://www.apple.com/macosx/x11/.

For pre-10.2 releases, you can use XDarwin http://www.xdarwin.org/.

For easy installation, look at the Fink Project, http://fink.sourceforge.net/. This brings Debian package management tools to MacOSX.