Integration with other apps

I am trying to incorporate a blog, a wiki, and bug tracking all into
my Rails webapp. Mephisto recommends starting with their whole app
and making certain pages static content, but this only takes care of
the blog part.

Essentially, my problem is not with Rails, but with the fact that all
of these other applications have no way of integrating with the
authentication, authorization, and session control in Rails. (Trac
may be even more difficult to integrate than Mephisto and any given
Rails-based app.)

Essentially, my question is: has anybody done single sign on work?
Considered ways to use the same stylesheets and layouts for more than
one project?