Discourse is the 100% open source discussion platform built for the next decade of the Internet. Use it as a mailing list, discussion forum, long-form chat room, and more!
Flarum is a delightfully simple discussion platform for your website. It's fast and easy to use, with all the features you need to run a successful community.
Murmur is a new tool for group communication that blends concepts from mailing lists, forums, and social media. Now members can choose how they receive emails and collaboratively moderate discussion.