http://peerjs.com/ is the best library I've found for WebRTC thus far. Their documentation is fair, there's decent support for DataChannels and they've also open sourced a signalling server. https://github.com/peers/peerjs-server
https://github.com/rtc-io/rtc-signaller
That said, it wouldn't take much to write an signalling client that followed the basics of the messaging format if you did want to roll your own:
https://github.com/rtc-io/rtc-signaller#signaller-message-ha...