I asked a question that got closed for not being suited for the Q&A format that RPG.SE uses, and was told that my question would work better on a discussion forum.
Where can I find an RPG discussion forum well suited to my question?
Guidance for answers
This should be a curated list of directions a question-asker could go, not a collection of forum reviews. To keep answers action-focused, I suggest:
Write answers with an eye to redirecting an off-topic question asker. The answers should quickly help someone decide where to take their closed question. Focus on creating a collection of signposts to help them choose the best site for their current question.
One site suggestion per answer. Well-regarded fora will float to the top, while ones that might be included for completeness but aren't popularly endorsed will fall to the bottom.
Avoid answers that focus on suggesting a forum for its own sake, or just exist because you think it's a good site.
Not all playstyles and personality types are good fits for every one of these forums; try to indicate the kind of player they cater to without being hostile/judgemental if that's not your cup of tea.