Parallels offers virtualization and automation solutions for desktops, servers, hosting, SaaS and more. Plesk is a commercial web hosting automation program provided by the same.
Plesk, like cPanel, is a web hosting control panel which can be used on shared, vps and dedicated hosting. It automates almost all the tasks for web hosting easily and efficient too, reducing operating costs and resources.
You can see more details from their website: http://www.parallels.com/products/plesk/