hosting and user/group management advice please

Hi,

Our department is looking for a hosting solution for our projects.
Most of them are Rails applications, but we have some Java apps as
well. We would like something like Slicehost, but really need some
kind of user/group management. We have admin users, project owners and
developers. The admin users should be able to control the "slices",
the project owners should be able to control only *their* slice*(s),
and the developers should be able to do a range of things, but limited
to what the project owner allows.

So I realize this might not be a hosting question, but if there
happens to be a hosting package (similar to Slicehost) that already
provides this, I'd love to know about it.

And if any of you know of a OSS web app that does this, I'd love to
hear about that too.

Thanks!

Matt