Patch Queue Manager (PQM) is a tool that is used to manage a branch via signed emails. This management typically includes receiving gnupg signed emails from authorized developers to merge their public branches.
PQM integrates well with test harnesses. For example, patch queue manager can be configured to refuse to accept a merge that breaks any existing test case. PQM can also be easily set up to report to other systems as well. Included is an example for emailing accepted merges to mailing lists.
The bzr-pqm plugin helps send these instructions from Bazaar.