I think the closest thing you'll get to "out of the box" for what you're looking for is Apache Cloudstack running on Citrix XenServer for a hypervisor.
With basic networking, you can keep things pretty simple. With advanced networking, you can allow your users to build virtual data centres.
It can be 100% free open-source software as well, although if you get Citrix CloudPlatform, you get a couple of extra features, and support, but you pay for the support.
You could be something similar with other products, but CloudStack actually has a pretty amazing amount of stuff that is just there already, and doesn't need configuring.