Ruby on Rails User Management Engine/Framework? (with web pages)

Hi,

There are quite a few post/recommendations re Rails authorization
plugins. What I'm asking here however is whether there is a
popular/good Ruby on Rails Engine (or framework) that includes the
user interface pages as well (and controllers/models etc). So
something one could integrate in (Engine) or use as a starting point
that includes:

- sign up (e.g. user creates a login, then email is sent with activation link)
- authentication
- authorization
- User interface allowing user to:
  - change password
- Delegated Administration (Optional)
  - supports multiple/separate companies/groups using the same application
  - Admin User for Company/Group X, and allocate access to Person Y
(create a new user)
  - UI to allow user to perform these functions

I threw in the last delegated administration as an optional extra. If
there a good/populate product that doesn't have this I'd rather hear
about it.

Thanks in advance