The virtualization API

libvirt is

A toolkit to interact with the virtualization capabilities of recent versions of Linux (and other OSes), see our project goals for details.
Free software available under the GNU Lesser General Public License.
A long term stable C API
A set of bindings for common languages
A CIM provider for the DMTF virtualization schema
A QMF agent for the AMQP/QPid messaging system
A technical meritocracy, in which participants gain influence over a project through recognition of their contributions.

libvirt supports

The KVM/QEMU Linux hypervisor
The Xen hypervisor on Linux and Solaris hosts.
The LXC Linux container system
The OpenVZ Linux container system
The User Mode Linux paravirtualized kernel
The VirtualBox hypervisor
The VMware ESX and GSX hypervisors
The VMware Workstation and Player hypervisors
The Microsoft Hyper-V hypervisor
The IBM PowerVM hypervisor
The Virtuozzo hypervisor
The Bhyve hypervisor
Virtual networks using bridging, NAT, VEPA and VN-LINK.
Storage on IDE/SCSI/USB disks, FibreChannel, LVM, iSCSI, NFS and filesystems

libvirt provides

Remote management using TLS encryption and x509 certificates
Remote management authenticating with Kerberos and SASL
Local access control using PolicyKit
Zero-conf discovery using Avahi multicast-DNS
Management of virtual machines, virtual networks and storage
Portable client API for Linux, Solaris and Windows