What about Discord[0]? I believe it uses it's own protocol, however there are already many unofficial API clients.

IRC-esque text chat, with Mumble-esque voice chat, with the best UX I've seen yet in a chat program[1]

[0] https://discord.gg/

[1] https://cdn.discordapp.com/attachments/115226319603630086/11...

Edit: s/seen ever/seen yet/, discord link