Backchannel Chat - Backchannel Chat is best in class discussion tool that is intended for teachers to streamline their class activities.
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
Eduflow - Digital learning that actually teaches students something
Groups.io - Email and web based discussion group software, includes archiving, emails, wiki, polls, file...
NowComment - NowComment is a complete suite of collaboration tools, streamlining group discussion, annotation, and curation of texts, images, and videos.
Gaggle Mail - Gaggle Mail is a simple and easy to use email list manager.