Development and status
Mailman 3 is essentially four main projects:
Mailman 3.0 is most suitable to new installations of Mailman. We do not guarantee that it will work well for migrations and upgrades of Mailman 2.x; we believe that will work, but encourage you to make backups and test your migrations first. It is not yet at full feature parity with Mailman 2.x, but we're working on that for 3.1.
See http://docs.mailman3.org/en/latest/index.html for installation information. There exists debian packages and Container Images for Mailman 3. The above mentioned link has more details about requirements, installation howto and such.