@marcus@k8s.social wrote https://marcusnoble.co.uk/2019-10-21-meetup-alternatives/ a few years back that may be of interest, in the IndieWeb community Aaron Parecki built https://github.com/aaronpk/meetable and it's been really great for what we need (including being used outside of the IndieWeb community such as for https://events.oauth.net/
by 
Jamie Tanna
.