http://genius.com/ http://genius.com/ has a literature section and allows you to annotate and discuss arbitrary web pages. If you are interested in building su

http://genius.com/ http://genius.com/ has a literature section and allows you to annotate and discuss arbitrary web pages. If you are interested in building such a product yourself and want to approach it more from the multiplayer document annotation platform angle than the specialized book forum angle the Memex, Ted Nelson's writing (especially Literary Machines) and Wikipedia's reference templates are also worthwhile sources of inspiration.