[jongdubois]

SocketCluster's API is similar to that of Pusher so it can be a good self-hosted alternative: http://socketcluster.io/ - It's also designed with scalability in mind. You do have to manage presence yourself though but that shouldn't be too difficult (You can keep track of user presence in your own database - That could actually be an advantage since you can go ahead and use that presence data easily on your back-end to do other stuff - Easy to integrate).

We're currently working with a couple of fast growing startups so it's getting traction (still early adopter stage though). We'll be announcing our native iOS client near the end of this week. (disclosure: I'm the main author)