Zelos - A very simple app for mobile teams - tasks and chats on desktop and mobile.
Proboards - ProBoards is a host of free forums with customer service.
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
ForumFree - ForumFree allows you to create a forum or a blog in a few simple steps.
Mailman 3 - Dedicated Mailman 3 installation. Unlimited lists/configuration. Free subdomain at mailman3.com. Dedicated support for list admins.
PlushForums - PlushForums is a modern online forum hosting platform.