Mobilizon is an event platform for the Fediverse which lets people and groups create events pages where participants can sign up, even if they don’t have an account. There’s lots more info on the official Mobilizon website ⧉.
Organisers can create a Mobilizon account on an existing server, or even start their own server if they prefer. Once an account is created, the organisers can use it to post event info pages where participants can say whether they are attending.
Mobilizon accounts can be followed from Mastodon etc, and when new events are added these will appear in followers’ timelines. They can then click through to the info page where they can find out more and say if they are interested.
I thought Mobilizon closed down?
No, it just changed maintainer. It was originally created and maintained by the non-profit Framasoft but is now maintained by another non-profit called Kaihuri. The switch was totally amicable, Framasoft just wanted to reduce the number of projects they oversee.