I see a lot of people using https://luma.com/. I'm sure it's not as big as Meetup but it does have a decent community of users, and you can set up pretty much anything with their free plan.
I had a good giggle when I opened their homepage and it looks exactly like the Performative-UI library[1] currently in the #1 spot.
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Luma doesn't do discoverability well unfortunately. Also very tech centric.
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