We use Matrix for our open source project: https://wiki.mathesar.org/en/community/matrix. We self-host a Synapse homeserver, but there's no reason why you can't set up a community on one of the big existing servers (e.g. matrix.org). Their Spaces feature allows you to package groups of channels together.

I set up Maubot for GitHub integration: https://github.com/maubot/github. There are moderation features, but we haven't had to use them.