He and Martin Sustrik both created ZeroMQ. Then after that, they saw some of the limits of ZMQ and created nanomsg. It's excited to see what cool stuff they were working on. It's a little hard to see ZeroMQ become abandonware from them. That said, the community is solid and supportive around ZeroMQ which actually I would say is the best part. In other words, you can tell if a project has staying power when the original creator no longer has to be there to maintain it.

I'll add that the AMQP 1.0 spec (supported in Rabbit using a plugin) is a peer-to-peer protocol that supports both the traditional broker use case, 'direct' p2p messaging and opens some interesting uses of message routers like Apache Qpid Dispatch Router.

I am no export but I have heard PH say, that it's much worse than the AMQP-0.9 Spec. It's a design-by-comitte thing, where he was sidelined.