@switchingsocial The only one I heard about is WanaWana (https://github.com/Psycojoker/wanawana). It looks like pre-alpha at this time, but the French advocacy group Framasoft announced plans to fund an alternative to MeetUp this year and this is one of the software they were considering for their future "framameet" service.
Yeah, I saw that in the degoogleify list, but it looks a bit abandoned? 😟
Registrations are closed for the moment.