libvirt provides an API for managing QEMU/KVM (and other hypervisors) exposed in C, Perl, Python, OCaml, Ruby, and Java, with bridges to AMQP/QMF and DMTF CIM.
virt-install, virt-clone, virt-convert a set of command line tools for provisioning new VMs from install media, existing VMs and appliances, respectively. See also 'virsh' command line shell with libvirt.
virt-manager, Virtual Machine Manager. A graphical desktop management app using libvirt. Can manage a single local host, or securely multiple remote hosts. Support QEMU, KVM, Xen and more
Ganeti, a cluster virtual server management software tool built on top of existing virtualization technologies such as Xen or KVM and other Open Source software.