The virt-manager application is a desktop user interface for managing virtual machines through libvirt. It primarily targets KVM VMs, but also manages Xen and LXC (linux containers).
To install on Ubuntu, run
apt-get install virt-manager
To connect to remote KVM or Xen server, you need to install libvirt on remote server.
On a CentOS Xen Server, i installed it with
yum -y install libvirt
Start libvirtd with
service libvirtd start
# service libvirtd status libvirtd (pid 18663) is running... #
Now you can connect to the server with virt-manager and create/manage Virtual Machines.