I run a community for people who run marketing services agencies. We didn't have an online forum, and things like Slack just didn't seem conducive to long-form,

I run a community for people who run marketing services agencies. We didn't have an online forum, and things like Slack just didn't seem conducive to long-form, quality discussion. I was very close to using some vBulletin type software, but we went with a platform called Guild which I can recommend. You have to pay for it, but there are no adverts and it's very smooth.