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