The Humane Environment is an open source alternative GUI in OS X, created by Jef "creator of the Mac" Raskin. Still in development and very much a proof-of-concept.

The Humane Environment (THE) is as easy to learn as a GUI (or easier) yet as fast to use (or faster) than the command-line systems we struggle to learn but love to use. It is easier to add new software to than any previous interface-based system.

Important observation: You cannot make an interface better without making it different (that's obvious). If it's a lot better, it will be a lot different. This means that it will feel unfamiliar to anybody familiar with present interfaces. Therefore, it has to be used for a while (after you read the manual) before you unlearn your present habits and can begin to appreciate it. You are in a worse position for learning it than a novice who has only to acquire new habits and has nothing to unlearn!

Link Discuss (Thanks, John!)