Wikibooks is great!
Wikibooks is a Wikimedia community for creating a free library of educational textbooks that anyone can edit.
Since the start in 2003, Wikibooks has grown to include over 35000 pages (year 2009) in a multitude of textbooks created by volunteers.
A great example of Wikibooks is the Wikibook Chess.
In exactly 12 chapters a variety of aspects like, Playing, Notating, Tactics, Strategies, Openings and Endgames, are clearly explained.
Wikibook of Actuarial Science
There is also a Wikibook of Actuarial Science. Although all the required chapters of 'Actuarial Science' are already there and structured, the content has to be taken care of.
So, if you like to contribute? Work for voluntary actuaries!