We've just open-sourced Pulsar! This is a pub-sub messaging solution with the necessary Yahoo scale, performance, and feature requirements to provide messaging as a hosted service, supporting a million topics.
Pulsar uses BookKeeper as the building block for the messages durable storage. You can find the announcement with more details at https://yahooeng.tumblr.com/post/150078336821/open-sourcing-pulsar-pub-sub-messaging-at-scale Pulsar code and development will be hosted from now on at https://github.com/yahoo/pulsar Matteo
