Isn't this a bit like saying: if it's for issue tracking, there's Bugzilla/trac/issuetracker/phabric, or if you need a wiki there's moinmon/mediawiki, or if you need a blog there's ghost/wordpress ?

More to the point: IRC (out-of-the-box) doesn't do archiving/search. Slack isn't self-host (which isn't an issue with people using github -- but it does introduce another vendor). Using external services forces you to maintain group membership, user-meta-data either in different user-databases, or via some form of federation.

No longer is removing a user/ssh-key from a github project enough to plug a hole in case of a hacked account.

Discourse isn't (that) bad -- but mailinglists are a lot better IMNHO. If you have a half-decent email program, like mutt, or even (al)pine.

At any rate, the ability to work via email (get bugs via email, close bugs via email) leverage what email is good at: off-line+synchronization. Which is one of the things git is good for. You know, distributed work.

> If it's for general discussions about the "future of the project" or bigger-picture topics, I'd use Discourse. It's a really nice way to organize discussions that are one step removed from code-related issues.

This is what is appealing and Github offering a builtin-to-github solution for it, with linking to Github accounts, autoformatting etc (like in issues) and so on. There is so much potential.