Caroline,
the Bug Tracker package can be configured to function as a task manager (yes the package name is now misleading). The workflow for these tasks is configurable.
Now, a projects has a set of tasks, so any new Project Tracker package would depend on the Bug Tracker package as it would use it for task management. The Bug Tracker depends on the Workflow package.
The Project Tracker package could also have a direct dependency on the Workflow package as project objects could be associated with workflows (i.e. a project goes through various stages).
Other types of objects mapped to a project object could be associated with their own specific types of workflows.
