WikiBooks: the open-content textbooks collection

What a great idea. There is a metric ton of information out there that doesn't belong in an encyclopedia but, have strong user communities willing if not wanting to share this stuff.

Essentially, this provides groups of people to collaboratively write books. I stumbled across this as I was looking for more information on a Python module and found Programming: Python.

See also:

Learn Mandarin Chinese
International Cookbook
GuitarSpace Invaders (The Textbook)