A couple of months ago I did a UX test of various free code platforms for promoting events, including Mobilizon, Gath, Gancio, and GetTogether. Reporting my experiences in a series of fediverse posts kicked off some insightful discussions with devs from a few of those projects, which may be of interest to anyone following this topic.
EDIT: the Zebras Unite network are working towards getting MeetUp.com to “exist to community”:
https://medium.com/@sexandstartups/meetup-to-the-people-how-a-zebra-could-rise-from-a-unicorns-fall-cfa93d83bcdc
EDIT: Here’s a list of free code projects working on MeetUp alternatives, some of which have already been discussed here, but some of the others may be interesting in federating social events: