Which underground communities do you visit (be it games, art, music, etc.)?
Don't feel bad if they don't overlap 100% with this space: as an example I frequently am on intfiction.org, as they are ace and fresh and innovative, even though they yet have to receive the Gospel of Free Software.
Good idea.
I'm using (mostly lurking on) Mastodon (.social), following some people, browsing some tags now and then.
Recently noticed the web revival movement (in fact via a certain blog post about a game called "Pete is Hungry") and I'm using melonland.net (a old fashioned bb-forum) as a gateway to it; don't be fooled about the obsession with nostalgia among some of the people there - there is some crazy creativity around.
I'm using some of the community functions of Itch.io.
My mailbox is also a bit active, I occasionally chat with some people.
A bit OT: I don't really dwell there, but do you know allegro.cc? Their board is a bit active, and there are many games in different stages of development. Have yet to find the time to take a few strolls there.
allegro is a fantastic place, and it warms my heart that it is still active after all those year (another proof that OSS outlasts proprietary suites, like XNA).