Question

These classes providing various global services to your application such as event handling, access to system settings, internationalization, etc.

QClipboard	Access to the window system clipboard
QDesktopWidget	Access to screen information on multi-head systems
QEvent	The base class of all event classes. Event objects contain event parameters
QFontDatabase	Information about the fonts available in the underlying window system
QMimeSourceFactory	Extensible provider of mime-typed data
QMutex	Access serialization between threads
QPixmapCache	Application-global cache for pixmaps
QSemaphore	Robust integer semaphore
QSessionManager	Access to the session manager
QThread	Platform-independent threads
QTranslator	Internationalization support for text output
QTranslatorMessage	Translator message and its properties
QWaitCondition	Allows waiting/waking for conditions between threads