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