OpenContent (Popularity: )
http://www.opencontent.org/ Reason for being: "facilitate the prolific creation of freely available, high-quality, well-maintained Content." Content = everything but software.
Classical MBA (Popularity: )
http://classicalmba.com/ Free lecture notes, articles, and resources pertaining to leveraging Open Source technologies and the classics in business.
Wikimedia Foundation (Popularity: )
http://wikimediafoundation.org/ International non-profit organization dedicated to encouraging the growth and development of free content, multilingual, wiki-based projects, and to providing the ...