https://uboachan.net is an interesting one centered around the surreal indie game Yume Nikki and it’s fan community
https://lainchan.org is similarly built around the fan community of Serial Experiments Lain, but also hosts a fair bit of tech discussion
https://chakai.org/tea/ has found an interesting solution to the problem of making feedback and conversation seem quicker and tighter in a small anonymous community, by only opening the board for an hour per day.