I've been building a Facebook Events style event organizing system for the Fediverse. It's based on the simple, open source, privacy-respecting event organizing tool https://gath.io

The attached video is a work-in-progress preview and shows compatibility with Mastodon. My hope is to get it working with lots of software, including stuff like Friendica that supports events and calendars.

Check out more at my Patreon: https://www.patreon.com/posts/organizing-on-32729070

Gathio

An easier, quicker, and much less privacy-invading way to make and share events

Also on the todo list is to add an Events tab to Hometown that keeps track of events you've RSVPed to. (For federation nerds: this will be driven by ActivityPub `Event` activities sent to a user's inbox after they've successfully RSVPed.)
@darius @mobilizon @mike maybe have a look at Mobilizon too? Activity pub events tool currently in development by french non-profit Framasoft