I know you're looking for a control panel for your users and not for yourself. It's not my intention to steer you to control panels for your use.

It's just that most of the control panel software that's fit for end users is comprehensive enough that it also features an admin console.

cPanel, Plesk, and the lot of them I mentioned have at least some control the end users can assert, and the whole panel infrastructure is already built. I thought those might offer a good basis for what you want to do.