Warichu is a social annotation tool that sits on top of the web and allows everyone to discuss the webs content. You can think of the situation as being similar to that of an ant colony mapping out the terrain it lives in - all the ants investigate here and there, finding useful resources, remembering the details and telling their friends so they can use the resources too. In this analogy the web is the terrain, and we are the ants! We communicate on a layer that overlays the web - a layer just for collaborative communication of information. That layer is the Warichu.
With Warichu you can create various types of virtual sticky note and attach them to web pages. Whenever you go back to that page, your note will appear - and if you send the note to some friends it will appear on the page for them too. Different types of sticky note fulfill different requirements - some can be shared with other people, some are stored locally on your computer, some allow you to modify the web page you stick them to, others allow you to conglomerate snippets of text from a page..
An API is included that allows developers to create their own types of content notes (eg, page highlights, annotations, blogging tools)