What is libvirt? Libvirt is an effort to come up with an API for all virtualization platforms. Plus, it does have an implementation (libvirtd) which other management programs can talk to. For example virsh and virt-manager are couple of tools which can talk to underlying virtualization platforms such as Xen and KVM through libvirt.

Going a step further than libvirt, OpenNebula eases the creation of networks, adding cluster nodes and deploying virtual machines. Also, OpenNebula comes with a scheduler which will deploy a given virtual machine on the cluster. Scheduling policies can be configured and if more complex policies are needed those can be created through Haizea. Haizea is a scheduler which can be plugged into OpenNebula. OpenNebula stores all these information in an SQLite database that can be accessed from any other programming language if those information needs to be pulled out. A nice to have feature would be an API that gives all kinds of information stored in the SQLite database.