Mobilizon - A free and federated tool to get our events off Facebook

Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.

Upcoming.org - A simple way to share and discover interesting events

DownToMeet - DownToMeet is a platform to organize, find, and attend group events.

Happer - Meet people & participate in activities, happier together

Openki - Platform where you can search, propose, take part, help organize or publish workshops, lectures...