Bazitis aims to make hosting bzr repos easier and safer. It manages multiple repositories under one user account, using SSH keys to identify users. End users do not need shell accounts on the server, they will talk to one shared account that will not let them run arbitraty commands.

Bazitis is a port of Gitosis, which does the same for the git VCS. You can get more information and the source code for Gitosis here: https://github.com/tv42/gitosis.

Instructions for using bazitis can be found here: http://vimtips.org/2008/11/25/bazitis-gitosis-bzr-baazar/