SZTAKI Desktop Grid (SZDG) is an extension of BOINC in order to make it more flexible, versatile and scalable in terms of enabling the interconnection of different BOINC projects and execution of parameter sweep applications from a generic, high level user interface without the intervention of the BOINC project administrator. The paper describes the main concepts and features of SZDG. Among the many novel features the two most important will be described in detail. First, the paper describes those extensions that enable the easy development and execution of parameter sweep applications on SZDGs. The second part of the paper describes how SZDGs can be organized into a hierarchical interconnection scheme that enables to use SZDGs as building blocks to create higher level SZDGs.