Hey there!
I started implementing SmartFox as a Plugin for Unreal. It’s still in very early stages because I haven’t got much time to work on it, but if some people are interested just drop me a pm and I can provide you with the source and some instructions.
SmartFox provides stuff like Area of Interest (send only packet’s to nearby player’s) and other helpful stuff. At the moment the Client API compiles with the newest Unreal Engine 4 Version and you can connect to a server via blueprints. I still try to figure out the best way of how to hook up events that can be processed by blueprints such as OnLogin, OnConnect etc. If someone is interested to help me out with the plugin he / she can contact me of course, too.
I’m currently using SmartFox for a commercial project (rather small) and it works great, it’s not on Unreal basis though. I can’t tell how it would scale up with lots of players, but they have papers about server architectures and stuff.