These classes are useful classes not fitting into any other category.
| QDoubleValidator | The QDoubleValidator class provides range checking of floating-point numbers. |
| QErrorMessage | The QErrorMessage class provides an error message display dialog. |
| QIntValidator | The QIntValidator class provides a validator that ensures a string contains a valid integer within a specified range. |
| QKeySequence | The QKeySequence class encapsulates a key sequence as used by shortcuts. |
| QLibraryInfo | The QLibraryInfo class provides information about the Qt library. |
| QMacPasteboardMime | The QMacPasteboardMime class maps open-standard MIME to Mac flavors. |
| QProcess | The QProcess class is used to start external programs and to communicate with them. |
| QRegExp | The QRegExp class provides pattern matching using regular expressions. |
| QRegExpValidator | The QRegExpValidator class is used to check a string against a regular expression. |
| QRubberBand | The QRubberBand class provides a rectangle or line that can indicate a selection or a boundary. |
| QSettings | The QSettings class provides persistent platform-independent application settings. |
| QSharedData | The QSharedData class is a base class for shared data objects. |
| QSharedDataPointer | The QSharedDataPointer class provides a pointer to a shared data object. |
| QSplashScreen | The QSplashScreen widget provides a splash screen that can be shown during application startup. |
| QUndoCommand | The QUndoCommand class is the base class of all commands stored on a QUndoStack. |
| QUndoGroup | The QUndoGroup class is a group of QUndoStack objects. |
| QUndoStack | The QUndoStack class is a stack of QUndoCommand objects. |
| QUndoView | The QUndoView class displays the contents of a QUndoStack. |
| QUrl | The QUrl class provides a convenient interface for working with URLs. |
| QUrlInfo | The QUrlInfo class stores information about URLs. |
| QUuid | The QUuid class stores a Universally Unique Identifier (UUID). |
| QValidator | The QValidator class provides validation of input text. |
| QVariant | The QVariant class acts like a union for the most common Qt data types. |
| QWindowsMime | The QWindowsMime class maps open-standard MIME to Window Clipboard formats. |
| Qt | The Qt namespace contains miscellaneous identifiers used throughout the Qt library. |