Zelos - A very simple app for mobile teams - tasks and chats on desktop and mobile.
Tendenci - Tendenci - The Open Source AMS is a cloud-based all-in-one management SaaS solution for Non-profits and Associations.
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
Kajabi - Kajabi is the only Knowledge Commerce platform today with everything you need to market, sell, and deliver your knowledge online.
Librelist - Librelist is a free as in freedom mailing list site for open source projects
WildApricot - WildApricot is a powerful cloud software to help you automate and simplify membership tasks.