Doctrine should support resources. This means that you can set-up a Doctrine server which serves many clients. The clients can request models and issue queries over the server. The client and server code should be *exactly* the same except for the connection handling.

Opening a resource connection:

$manager->openConnection('resource:www.someDoctrineResource.com');

Requesting models:

$manager->requestModels(array('User', 'Group'));

When the models are requested they can be used as if they where defined in the local scope. Basically Doctrine will then request the definitions for those models from the server and import the classes to the local scope (possibly by generating code).

$users = $conn->query('FROM User u');