Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
Mailman - Mailman is free software for managing electronic mail discussion and e-newsletter lists.
TidyHQ - Organization management tool to support membership, subscriptions, event planning, and outreach.
Mailman 3 - Dedicated Mailman 3 installation. Unlimited lists/configuration. Free subdomain at mailman3.com. Dedicated support for list admins.
Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.
MailChimp - MailChimp is the best way to design, send, and share email newsletters.