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

Geneva - An all-in-one communication app for groups & communities

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

Circle.so - Bring together your discussions, memberships, and content. Integrate a thriving community wherever your audience is, all under your own brand.

Get Together - Get Together is an open source event manager for local communities.

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