Wikibooks and Wikiversity

Wikibooks is a Wikimedia community for creating a free library of educational textbooks that anyone can edit. Wikibooks began on July 10, 2003; since then Wikibooks has grown to include over 34,084 pages in a multitude of textbooks created by volunteers.

Url: http://en.wikibooks.org/wiki/Main_Page


Wikiversity is a Wikimedia Foundation project devoted to learning resources, learning projects, and research for use in all levels, types, and styles of education from pre-school to university, including professional training and informal learning. They invite teachers, students, and
researchers to join in creating open educational resources and collaborative learning communities.

Url: http://en.wikiversity.org/wiki/Wikiversity:Main_Page

One can find various technical books and projects on these two Wikipedia's
Sister Projects and that also free of cost.