Currently I'm using a Decentralized Shared Mainline Repository. Here's my recipe...
You will of course need a server that's accessible to everyone.
Create a group for project.
$> groupadd projectname
Create an login for each of the users who will have commit access to the shared mainline.
$> adduser --ingroup projectname username
Create a directory for the repostitory inside the web servers document root
$> mkdir /var/bzr/projectname
Set the project folders group to the project groups name
$> chown :projectname /var/bzr/projectname
Set the project folders permissions
$> chmod ug+rwx,g+s,o+rx,o-w projectname
Now you can push updates
$> bzr push bzr+ssh://hostname/var/bzr/projectname
If you need to provide anonymous access to the repository one way would be to serve it with Apache.
Alias /bzr "/var/bzr"
Options +Indexes +MultiViews +FollowSymLinks
Allow from all
This would allow you to do something like this
$> bzr branch http://hostname/bzr/projectname