I was very excited about Mongrel2 for awhile, and also some of the projects that were being built off of it. For instance, I have mostly abandoned PHP, but Photon was the one PHP project that struck me as interesting, and it was built on top of Mongrel2. http://www.photon-project.com/
When I look here it seems the bulk of the work stopped almost 2 years ago:
https://github.com/zedshaw/mongrel2
The work done this last year seems minor. I also notice that Zed Shaw is mostly working on some Javascript library right now.
The world needs a great server built on top of ZeroMQ. Is anyone still focused on this project? If not, are there any other servers that use ZeroMQ in such a foundational way?