I've been using Arena for the last year or two: http://are.na http://are.na. It's conceptually based on blocks and channels, where a block is text, pdf, video,

I've been using Arena for the last year or two: http://are.na http://are.na. It's conceptually based on blocks and channels, where a block is text, pdf, video, audio, image, etc. and a channel is an ordered set of blocks and other channels. Channels can be public, private, or private with collaborators. It's web-based and has a good API(1), which I use as a lightweight CMS for my own website. They plan(2) to eventually charge for a pro version, but for now they are accepting rewarded donations. (1) http://dev.are.na/documentation/channels http://dev.are.na/documentation/channels (2) http://future.are.na/ http://future.are.na/