A forum is an important brick to build a strong community around a project, a website, etc… and probably the most popular opensource forum platform is PhpBB, followed by Vanilla and many more. Great projects, well maintained, big community around, etc… but with a traditional approach of a forum.
– Allows the community to moderate directly itself with a trust and flagging systems,
– Is optimized for reading (no next page/previous page, simply scroll down/up to read the content, it will dynamically update the page),
– Get advanced image handling (drag and drop, automatic thumbnail,…)
– Social Media Integration (1 click to share post to social media)
– Spam Blocking
– 1 click upgrade
– Single Sign On
– Search Engine Optimized
and many many more.
You can directly try discourse here.
NB: It sounds they are in a middle of “management crisis” with several leaders leaving the project for various reasons. The development might slow down but you should still have a good support from the community.