Modular applications

Hello everybody,

I've just started studying Rails and I love it already for its simple,
pragmatic spirit and the effectiveness and productivity that its
approach brings.
I'm thinking about building new applications on top of it and about
rebuilding existing J2EE applications in Rails as well, but I've come
across an architectural problem: we need to structure applications
into functional modules, each comprising any artifacts needed for the
additional functionality to work and interact flowlessly with the rest
of the application. The modules need to have clean interfaces and
dependencies between them, so that we can build and distribute
different "variants" of the application (e.g. basic edition,
management edition etc.).
How would you proceed and/or what (existing or additional) tools would
you use in order to do so? I'm really interested about both
application structuring and build and deployment processes and tools
advice. I'm interested in the development process as well, because it
would be highly desirable for developers not to keep the whole
application in their development workspace, but only the modules on
which they actually work (and their dependencies of course).

Is the Rails Engines plugin the way to go? Would it satisfy all
requirements?

Thanks in advance.

Fabio