OS X Hypervisor Framework

It looks like Apple has added system APIs for user space hypervisors. The APIs might even be compliant with Mac App Store regulations.

Check out the Hypervisor Framework and  vmnet Framework.

The xhyve project (started by Michael Steil) is a port of bhyve (the FreeBSD hypervisor project) to work with these new APIs.

Unfortunately, the use of the com.apple.vm.* entitlements seems to be restricted to Mac App Store apps only.  I have not seen any documentation on how to obtain the relevant entitlements.