There is probably little to say about this. Thelemapedia is the “wikipedia-like” encyclopedia of Thelema and Magick focusing on the works and philosophy of Aleister Crowley. Yet another excellent project of the Scarlet Woman Lodge. Hundreds of articles to get you started.
Right now I’m aware of two forks (some content has been copied and/or modified under license from the aforementioned site) of Thelemapedia of some significance: The Free Encyclopedia of Thelema and LAShTAL.com‘s version, the Encyclopedia Thelemica.