Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Taskade - Make lists, organize your thoughts, and be inspired to get things done. Taskade is a collaborative space for your tasks.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
The New Dropbox - Enterprise software portal for team collaboration
Bigtent - BigTent is a web-based organization and communication portal for groups.
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.