Isn't Eventbrite also a valid alternative, that has the advantage of bing a mature, feature-rich offering? Free events are free, and their profits come from supporting paid events.
The FreeCodeCamp one is pitched as a self-hosted solution, which means it won't have a network of meetup groups like meetup.com does. If you have a big network of meetups yourself (like, say, FreeCodeCamp), then sure it works. If you're just a small meetup group, it'll be no better than just hoping people find your site on google as is.
I've never heard of them either. Meetup's demise will be a great opportunity for them, but I think a lot of them will be hobbled by having off-putting names.
https://emamo.com
https://kommunity.com
https://joinmobilizon.org/en
https://cete.io (not yet launched?)
https://eventy.io (not yet launched)
And the not-yet-build one by FreeCodeCamp: https://twitter.com/ossia/status/1183845054449930241
I've never heard of any of them. Opinions?