Yeah I recently discovered enet through Emscripten (which emulates UDP on top of SCTP. SCTP is the protocol used by WebRTC and supports reliable and unreliable packets like enet and RakNet, though I believe Emscripten's UDP emulation only uses it in unreliable mode (since UDP is unreliable).

Apparently SCTP can be tunnelled over UDP if native support is unavailable (which seems very likely), which means I've ended up with the crazy stack of:

enet, which uses UDP which is emulated using SCTP which is tunnelled through UDP.

Crazy but it works. Bring on the real time web games!