Fediverse

I know there is mobilzon but mobilzon is a meetup.com clone whereas evite is different.

Evite you can create an event and invite people via email or send them a link. They can rsvp and add it to their calendars.

Come of these features are covered by mobilzon but not quite. Evite doesn't require you make a group or add people to the group as members. It's a little more atomic. Honestly I think it's a good deal more flexible than the meetup/mobilzon design pattern.