Robin Good: Connexions is a place to view and share educational material made of small knowledge chunks called modules that can be organized as courses, books, reports, etc.
Anyone may view or contribute: authors create and collaborate, instructors rapidly build and share custom collections, learners find and explore content.
From the official site:
"Lenses enable both organizations and individuals to give their stamps of approval to content in the repository, allowing for user-driven quality control of modules and collections.
Through these lenses, users can provide their own tags and comments for items in the repository. Lenses can also be used as "bookmarks" within the repository to keep track of related or otherwise interesting content."
More info: http://cnx.org/