How can I set up an email discussion list based on CiviCRM groups?
we have deployed this in a couple of situations including making a UI that let's you set the Civi Group, or a Civi Relationship, as the basis for the Mailman group. There is still the issue about what happens when someone unsubs via Mailman, since the Civi synch just puts them back in ;-)

I don't think we were ever able to take it further than a build for that single client ie it didn't not get developed as an extension or even a releasable module. i should check what might be involved in making it able to be shared.