Great to see this. Being able to run your own Pusher-compatible server sounds quite useful for dev environments or internal usage. Is Poxa endorsed by Pusher at all?
FWIW, our company, Fanout (https://fanout.io), is similar to Pusher except we decided to open source our own code to be good citizens. No need for the community to reverse engineer anything. ;)
Since there are already a bunch of open source "push" servers (Socket.io, Faye, Firehose, etc), I assumed the main draw of Poxa would be to use as a substitution for the official Pusher cloud service depending on deployment scenarios.
Of course, someone could certainly use Poxa without any intention of ever using Pusher.com. The protocol features & client libraries are very nice.
Ruby - Slanger* (https://github.com/stevegraham/slanger)
Java/Play - PushPlay (https://github.com/danbeaulieu/PushPlay)
*Disclosure: I am one of the authors of Slanger.