<a href="http:&#x2F;&#x2F;genius.com&#x2F;" rel="nofollow">http:&#x2F;&#x2F;genius.com&#x2F;</a> has a literature section and allows you to annotate and discuss arbitrary web pages.<p>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&#x27;s writing (especially <i>Literary Machines</i>) and Wikipedia&#x27;s reference templates are also worthwhile sources of inspiration.