Mobilizon - A free and federated tool to get our events off Facebook
Taskade - Make lists, organize your thoughts, and be inspired to get things done. Taskade is a collaborative space for your tasks.
DownToMeet - DownToMeet is a platform to organize, find, and attend group events.
The New Dropbox - Enterprise software portal for team collaboration
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
P2 - Share, discuss, and collab with your team. By Wordpress.