We used Unity3D with Photon as a network framework. Bundle Unity3D + Photon works on both mobile devices, desktops and WebGL from the box.
But in our case, we practically hardly refactored the Photon, leaving only the transport protocol. Let's just say... its to massive...
And what about the Unity, well, a little knowledge in Java, ObjC, C++ and JavaScript should be enough to cope with the pain of cross-platform difficulties