Parallels Virtuozzo is a patented OS virtualization system. It provides an advanced control panel that offers individual users with a limited functionality set on their own client panel.
With Virtuozzo, you can manage your container or isolated partition on an OS instance and a single server with maximum efficiency. You can start, stop, reload, reboot and do various other things to the container itself. It is also possible to install new software, view resource usage and restart services with Virtuozzo.
However, you will still require Plesk or cPanel or WHM for managing operations in your account like creating new accounts and adding new domains. Virtuozzo is only used for dividing a server into containers, for providing performance isolation, for dynamic resource allocation and for mass management. But Plesk or cPanel is utilized for hosting operations performed on a daily basis.