Sorry about this.
And by “this” I mean listing almost every active forum I’m aware of.
I couldn’t figure out how to edit the original post, and a lot of my descriptions are bad, so somebody else do it. Write better descriptions if you’re more familiar with these sites than me. Somehow these results are curated - I also know dead forums, I know forums which get five posts a year, I know really bad forums, I know things.
The Straight Dope forums - A general forum spun-off from the eponymous question-and-answer newspaper column turned website.
GBATemp - A gaming forum, with a focus on video game modding, homebrew, and hacking.
Romhacking dot Net forums - A forum for general game romhacking.
Something Awful - ten bux
Fark - News and current affairs link aggregator and discussion. It’s not news, its Fark.
Duke4- Unofficial Duke Nukem fan forum.
Deltarune Unofficial Message Boards - Unofficial Undertale and Deltarune fan forum.
Larian Studios Forum - Official Larian forum. Larian are the developers of videogames like the Divinity series and Balder’s Gate 3.
Vintage Story Forums - Official Vintage Story forum. Vintage Story is a voxel-based sandbox survival game inspired by and often compared to Minecraft. The forums focus on discussion of the game, including storytelling and modding.
Bay 12 Games Forum - Official forum for Bay 12 Games, mostly focused on their best-known title, Dwarf Fortress. Storytelling with Dwarf Fortress is a particular interest members have.
Adventure Game Hotspot Forum - Adventure game fan forum. Spiritual successor to the now defunct Adventure Gamers forum, if you remember that one. For all adventure games old and new, but I won’t lie the userbase skews mostly towards old 80s/90s Sierra and Lucasarts adventure games.
Mix ‘n’ Mojo - Another adventure game fan forum, focused on 80’s/90’s LucasArts games like Monkey Island, Sam and Max, and the Indiana Jones adventure games.
Minecraft Forum - Once official, but now unofficial Minecraft forum. Minecraft is a voxel-based sandbox game, and needs no introduction.
Planet Minecraft - Unofficial Minecraft forum focused on creating skins and datapacks for others to enjoy. Userbase skews younger.
Pokemon Community Forums - Official Pokemon forum. Skews young, with strict moderation which only lets you discuss official Pokemon products in an all-ages corporate friendly way. If you can live with this, its a fine place for official Pokemon related discussion.
Pokecommunity - Unofficial Pokemon fan forum, with general Pokemon discussion and a strong romhacking community.
Seribii dot Net Forums - Unofficial Pokemon fan forum, which is general but ends up leaning towards game guides and Pokemon anime discussion.
Eevee Expo - Pokemon fan game forum, focusing on a suite of tools called Pokemon Essentials. Unofficial to the Pokemon franchise, but official to the Pokemon Essentials dev team.
Kanzenshuu the Forum - Dragon Ball Z franchise fan forum. I only know it as the home of high-effort anime fan cuts, but it probably has other things going for it, somebody else write the blurb.
SMW Central Forum - Forum for Super Mario World Central, a romhacking site. You can find romhacks tutorials resources u know the stuff.
TASVideos Forum - Forum for TASVideos, a form of videogame superplay using emulator tools. Each game has its own megathread where users post new discoveries and WIP TASes.
Startrek dot Website - A forum for fans of Star Trek and/or Doctor Who.
Sims 4 Studio - A forum for Sims 4 modding tool Sims 4 Studio. Contains discussions, tutorials, and showcases of Sims modding.
Vivaldi Community - Official forum for the Vivaldi web browser.
Ace Attorney Online - Ace Attorney fan forum dedicated to the eponymous fancase maker Ace Attorney Online. Lots of fan game discussion, not so much source material discussion. Has boards for French, Spanish, and Dutch speakers, but those are significantly less active than the English language boards.
RPG Maker Web Forums - Official forum for the RPG Maker series of software. Contains discussion of RPG Maker gamedev, and free assets for devs to use.
Starmen dot Net Forums - Forums for the unofficial Earthbound fansite Starmen, which contain discussions of those games. Also hosts an official Undertale section, but the Undertale discussion here is significantly less active than on the Deltaboards fansite.
TIGForums - Forums of the Independent Gaming Source (TIGSource). Long-running general independent gamedev discussion forum.
Gaia Online - A long running general/anime/roleplay forum where users create their own character with items purchased from their virtual shop.
Recolor Me - A general forum inspired by Gaia Online, where you also create your own character with items purchased from a virtual shop. They call these avatar sites, you know.
Blender Artists - Unofficial art discussion forum for the users of the Blender 3D software.
Krita Artists - Official art discussion forum for users of the Krita digital illustration software.
Aesprite - Official art discussion forum for users of the Aesprite pixel art software.
Inkscape Forum - Official art discussion forum for users of the Inkscape vector illustration software.
Dragon’s Den - Unofficial Dragon Quest fan forum.
Discourse Meta - An support forum for the Discourse forums software.
Mario Boards - Unofficial discussion of the Super Mario franchise, and general gaming discussion.
No Homer’s Club - Unofficial The Simpsons fan forum.
Linus Tech Tips - Official forum for the Linus Tech Tips Youtube channel.
Ars Open Forum - Forum for Ars Technica, a tech news website.
The Deviantart Forum - Forum for users of the art site Deviantart.
Proboards Support - The support forum of forum hosting provider Proboards.
The LifeStream - Unofficial Final Fantasy VII forum.