In the cisco web say that:
"Inside the base-level VM, you can run a number of different images. At this time, you can load IOS XR, IOS XE (via the CSR1000v), IOSv, as well as generic server images such as Ubuntu Linux. Some noticeable absences are the adaptive security appliance (ASA) and any kind of Layer 2 device."
"The base OS of the CML image is Ubuntu Linux, the hypervisor is kernel-based virtual machines, and OpenStack Grizzly handles the VM orchestration. Cisco-proprietary pieces take over to handle the middleware layer (Service Topology Director) and user interface (Maestro is the working project name), with the configuration engine following on in the guise of AutoNetKit with several Cisco extensions added."
You can install and run different Virutal Machines inside CML.