The extended system tray (xSysTray) is a plugin for XCenter/eCenter that provides support for the system tray area in the XCenter/eCenter bar. This area, also called as the notification or indicator area, is commonly used by long running applications to display their status using graphical icons and to provide a way to control these applications by clicking on their icons.
There is a number of other tools to implement the described functionality. The main reason to create another implementation is that existing ones do not provide the level of functionality required by the QT Toolkit for which this extended implementation was created for.
Since the SysTray/WPS API is being already used by a number of applications to implement system tray icons, the extended System Tray widget implements this API as well to provide backward compatibility.