A Patch Queue Manager (PQM) is a program that sits on top of a repository (or set of repositories) and handles all kind of write access to it according to a set of policies like:

- who is allowed to commit (security) - when access is opened (for release engineering tasks) - which branches are open and to whom - generate commit messages - handle merge request from remote repositories (for synchronisation) - and so on…

The nice thing is that a PQM can be VCS-neutral (although a centralised VCS doesn't need such a system).

The one I know of is the Bazaar one, inherited from Arch/tla days written by Robert Collins and now maintained through his work at [http://canonical.com Canonical]. The repository can be found here: [http://people.ubuntu.com/~robertc/pqm/trunk/ PQM repository in bzr format]