Not the ‘community’ you enjoy the most but the free, as in beer, self hosted, free and open-source forum software used to run it, which could be an awful community with a fantastic software.
Not sure it's my favorite, bur definitely the most used: <a href="https://www.discourse.org/" rel="nofollow">https://www.discourse.org/</a><p>A more recent alternative is <a href="https://flarum.org/" rel="nofollow">https://flarum.org/</a>