Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.

TidyHQ - Organization management tool to support membership, subscriptions, event planning, and outreach.

Groups.io - Email and web based discussion group software, includes archiving, emails, wiki, polls, file...

Gaggle Mail - Gaggle Mail is a simple and easy to use email list manager.

NationBuilder - The world's first platform for leaders, handcrafted from scratch to help you grow your community and lead them to action.

Mailman - Mailman is free software for managing electronic mail discussion and e-newsletter lists.