What are some alternatives?
Openki - Platform where you can search, propose, take part, help organize or publish workshops, lectures...
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Guestboard - Lead powerfully-organized group events with Guestboard – a modular event platform that gives groups of 10-1000+ people a central space to coordinate, build excitement, and save money. No more crazy email threads. No more massive group texts.
Eventbrite - Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Get Together - Get Together is an open source event manager for local communities.
DownToMeet - DownToMeet is a platform to organize, find, and attend group events.