I'm surprised nobody's mentioned Google Groups, no it doesn't have any deep integration with GitHub, but plenty of very active projects hosted on GitHub and els

I'm surprised nobody's mentioned Google Groups, no it doesn't have any deep integration with GitHub, but plenty of very active projects hosted on GitHub and elsewhere use it, and it's a great free forum provider with an easy web UI for those that want it, and E-Mail for power-users. Keep in mind that most of the value people get out of such forums is being able to search possibly years old posts after the fact, and something like E-Mail is much more likely to be useful in that fashion than some glorified IRC client.