Zelos - A very simple app for mobile teams - tasks and chats on desktop and mobile.
Mailman - Mailman is free software for managing electronic mail discussion and e-newsletter lists.
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
Mailing Group - Listserv - Allows you to run a free Listserv or email group right from your WordPress dashboard.
Librelist - Librelist is a free as in freedom mailing list site for open source projects
Mailman 3 - Dedicated Mailman 3 installation. Unlimited lists/configuration. Free subdomain at mailman3.com. Dedicated support for list admins.