JK Rowling announces 'Pottermore' collaborative fiction website

It's not clear whether it's a game, online book, collaborative reading experience, collaborative writing experience, social network for Potter fans, or all of these things, but there are some image assets from the comments on the Guardian article that give an idea of what the website will look like:

http://assets.pottermore.com/emcp/downloads/pottermore_gateg...

http://assets.pottermore.com/emcp/downloads/pottermore_hogwa...

http://assets.pottermore.com/emcp/downloads/pottermore_chess...

http://assets.pottermore.com/emcp/downloads/pottermore_xmash...