Mobilizon is a free open source federated events platform, designed to provide a privacy-friendly alternative to Facebook Events. You can follow at:
It has just left beta testing and is now ready for use. You can find out more on official sites at:
It has been designed for activists and volunteer organisations, but anyone can use it.
Mobilizon uses ActivityPub to federate, as does Mastodon.
I don't know whether Mobilizon is compatible with Mastodon yet, but I think part of the reason for them using ActivityPub was to make such a thing possible in the future?
It's made by Framasoft who also make PeerTube, and that definitely is Mastodon-compatible nowadays.
This is a brand new server run by the main developers of the project as a spin-off of mastodon.social It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!