This article is from the MachTen & CodeBuilder FAQ, by Jaime Julca firstname.lastname@example.org with numerous contributions by others.
A Macintosh running MachTen or CodeBuilder appears simultaneously as a
traditional UNIX system with multiple windows and a Berkeley command line
interface, and as a traditional Macintosh system with a Finder interface. If
you pull down the System application menu when MachTen or CodeBuilder is
running, you can click on Finder, any Macintosh application, or
MachTen/CodeBuilder. If X is running, you have an X desktop as well which
you can customize with OpenLook, Motif and even AfterStep window managers.
You can easily toggle back and forth between Finder, Mac apps, the UNIX
desktop and the X desktop.