HyperKitty, the Mailman archiver
HyperKitty is the archiver project for the Mailman 3 suite, allowing users to browse mailing lists, start new threads and reply to existing threads, mark messages as favorite, search archives, and so on. It is a Django-based web application that aims to implement modern archiving. It can also run standalone, without the rest of the Mailman suite, to serve as a web forum. It was originally started by the Fedora community.
You can read the main documentation online. If you want to preview it, there are two demo servers (1, 2) available. They are development servers, so they may be broken or obsolete at the time you access them. It's usually OK, though.
HyperKitty, being a Django application, can be used with any other Django project. If you are deploying HyperKitty standalone, you'll only need hyperkitty and hyperkitty_standalone.
We've done some usability testing on HyperKitty.
Design mockups are available at: http://linuxgrrl.com/fedora-ux/Projects/Mailman/Prototype%201/
More designs are available as blog posts: