I’m on a tennis forum that has many sub-forums on all different topics. I post on the main forum and on the non tennis subforum on the politics thread.
Lots of bogleheads here!
I have been a part of a couple other boards, one or two for several years…but most of those have turned into FB groups - which is fine. CC is my main board. Not a board, but I also spend a good bit of time on Twitter for personal and professional information. Big Twitter fan.
My newest obsession is watching the Instagram stories of a few people I really enjoy on Instagram - I guess it’s not the back and forth banter - mostly me taking in their banter - but I equate it to being similar to a message board in that I look forward (usually at night before bedtime) heading into their story and seeing what they had to say today.
There’s a sprawling one that started out for DC parents, but now has multiple topics and people from all over. It’s anonymous, so it can get pretty nasty, and I keep swearing I will not go back to it. But it’s somehow addicting as well, and I have gotten a lot of helpful information and advice.
But I feel like CC parents are more my peers; I’m aging out of the parenting board and sometimes feel ancient as a mid-50-something there.
I have two other boards that I visit- one is a political discussion board for democrats and one is a personal finance board. I spend more time at the political board than here.
I post on three other forums, one a cruise forum, one a travel forum, and one a well-known amusement park forum, so pretty much all three are intertwined with travel.
I am still on a (dwindling) forum that covered a wide WIDE variety of topics. It used to have hundreds and hundreds of posts a day. Now, less than 20. I first started there around 1997-98 when I was trying to get pregnant. I was so happy to find CC because it filled up my time/need for a general forum (and hey learning about college is good too!).
I’ve been active (as a poster or just a reader) on several forums. My kids are adopted so I was active with the adoption community for many years, but I’ve kind of lost interest since my my kids are all are nearing adulthood and we have no intention of adopting again. You would think that adoption forums would be kind and supportive - but, man, there was tons of drama and lots of just plain nasty people on those forums.
I read comments (but don’t post often) on many other different types of forums - they are my go-to source when I need information on something like travel, health, city info, etc.
I’m active on several FB groups that are moderated well and enjoy those. I was a member of my local community’s FB page and found it very helpful (I could post a question about school policies, or local activities, etc. and within seconds I’d have an answer), but I had to quit that one because some members made it their full time job to be jerks and cause drama. I just don’t get those people.
My favorite forum was one for PT Cruiser owners/fanatics that I joined when mine was having problems (and I felt like our mechanic was charging us way too much for the repairs). Nicest bunch of guys ever - and they knew I was female. There was one man who told me to PM him and he’d give me his phone number so I could call him and he’d help me with the problem - basically teach me how to fix it. I was like - What??? I politely declined explaining I didn’t feel comfortable doing that, but I got PM’s from other members telling me that the guy was just a really helpful fellow and a couple of them had gone to his home where he had helped them repair their cars for free. I still didn’t call him - I just didn’t feel right about it, but they were incredibly nice and helpful to a mechanically challenged female.
I like the Quora forum - I find it very interesting and entertaining, but I don’t post as you can’t be anonymous.
I like CC, the overwhelming majority of people here are kind and pleasant. I have a hard time relating to some of the members - I kind of feel intimidated sometimes, there are some sub-forums (and threads) that I just don’t choose to visit as I would be a fish out of water, but I’ve enjoyed my experience so far (I’ve been a member for a little over a year I think).
I rarely post n other boards, but on an active professional list serve. When I was redoing kitchen, I liked that group. However, that group is now under Houz, and is harder to navigate. My son’s school has a FB group, then another political group. The latter is is often very interesting. But CC is the best. When I couldn’t visit CC for a week, I missed it.
I like etiquettehell.com
No. I do not post on Facebook or any other social medium except for this one. This is my crazy obsession. I guess I will have to find a new hobby once my son’s admissions process is over!
Maybe it has something to do with the ruthless moderation. 
Oh, I don’t think so! There would be a lot fewer posters if we quit at that point!
A couple of Jamaica-related ones and CC, that’s it.
I stop in on a higher ed forum every month or so and another local forum for my city (but that one isn’t very active.)
I was very active on a parenting of young children board way back in the day and I still have friends in real life from that one who get together and remember fondly some of the crazy characters and crazy stories from there. I may have mentioned this before, but a very opinionated poster posted pictures of her kid’s first day of preschool with kid standing in front of the preschool sign and someone who didn’t like the poster contacted the preschool pretending to be the mom and withdrew her kid from preschool. I still laugh now about it. And someone who worked at Drugstore.com seemed to be posting all day from work showing pictures of all the freebies she was scoring and someone who knew her name contacted her employer to invite him or her to the site to see how often this employee was posting. Then the employee got fired. In the old days it seemed like we were more trusting about online connections. I wonder if some of these moms are still out there stirring a different pot.
I’m active on a wedding board.
Yes, I’m part of a professional forum that I read daily. I don’t post much there, but it has served me well over many years. As a solo practitioner, I have benefited greatly from having so many resources literally at my fingertips.
I also read student doctor, but don’t post and haven’t joined.
I used to be active in a usenet group devoted to mysteries (rec.arts.mystery) before the existence of the WWW. We ultimately discussed everything and anything, especially politics. 
As it became more and more difficult to find a decent newsreader, the RAMily mostly migrated to FB. There are people I “met” there with whom I’ve been friends since 1994.
I participated in a listserv dedicated to Dorothy Dunnett, another to Partick O’Brian, and rec.sf.written (where discussion was a blood sport ). I particicpated in a diabetes group for a while, but gave it up because it was dominated by some really strange and/or hostile people. I did learn a lot there, though.
I remember the old AOL boards fondly. I don’t post or participate on any other forums. Just CC. Sometimes, if I’m looking for some information, I’ll end up on a board or forum to get info, but not as a regular participant.
I am active on a couple of running forums. I was permanently banned from the main one (women) that I was on. I wasn’t a fan favorite because I actually was disciplined and held myself accountable in life and with my running/health. It had deteriorated into mainly being a bunch of whiners who didn’t even actually run anymore, and the expectation was that you could only post in a way that blew sunshine up everyone’s posterior.
I follow a few other athletic sites related to a college sports team I follow and post occasionally.
So how does one FIND other interesting forums?