explorer like tree view in rails ?


I am looking for recommendations on a plugin or javascript lib that
support building an explorer type tree view. I am somewhat afraid that
the more extensive things available are fairly complex, and we want to
use something free ..

I am using acts_as_tree and creating entries from file directories and
then displaying some of that info on a web portal with special custom
functionality that we need for our app.

I need to be able to build leaves of the tree on the fly with ajax as
well since creating the whole tree may take too long etc.

Thanks ..