Mailman - Mailman is free software for managing electronic mail discussion and e-newsletter lists.
Mailing Group - Listserv - Allows you to run a free Listserv or email group right from your WordPress dashboard.
Mailman 3 - Dedicated Mailman 3 installation. Unlimited lists/configuration. Free subdomain at mailman3.com. Dedicated support for list admins.
Listmonk - Send e-mail campaigns from a powerful dashboard. High performance and features packed into one app.
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
Sendy - Sendy is a self hosted newsletter app that sends emails 100x cheaper via Amazon SES