I like Discourse too. (better than all the others mentioned so far)
There's also Talkyard. It's a bit like Discourse, and has Slack chat features (maybe nice with informal chat channels?) and StackOverflow like Q&A topics. I'm developing it. Open source & beta. https://www.talkyard.io/forum/
Nothing is wrong with it, it's just a different interpretation of forums that is a departure from the "classic" bulletin boards we are discussing here.
Here are some more ideas: https://github.com/Kickball/awesome-selfhosted#social-networ...
Flarum looks like a worthwhile option: http://flarum.org/