Zelos - A very simple app for mobile teams - tasks and chats on desktop and mobile.
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Mailman 3 - Dedicated Mailman 3 installation. Unlimited lists/configuration. Free subdomain at mailman3.com. Dedicated support for list admins.
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Mailman - Mailman is free software for managing electronic mail discussion and e-newsletter lists.