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.
Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
Bigtent - BigTent is a web-based organization and communication portal for groups.
Slack - A messaging app for teams who see through the Earth!
Nabble - Nabble is a forum software that are embeddable and fully customizable with scripting language.