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.
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
Mobilizon - A free and federated tool to get our events off Facebook
Membee - Membee is web-based membership management software.
Get Together - Get Together is an open source event manager for local communities.
Galette - Galette is a membership management web application towards non profit organizations.