I would like to add two apps which uses libvirt the site.
Ruby Objects for libvirt
based on top of the native ruby binding, Virt ruby gem exposes real objects such as Host, Guest, StoragePool, Interface etc.
Foreman - Web UI for provisioning and managing servers
Among the many things foreman can do, It provides to relevant parts to libvirt:
UI to list / start / stop / destroy vms
UI to create a new vm as part of the provisioning process (e.g. dhcp, dns, tftp, pxe, vm, ks/preseed, puppet etc)