This is the list of demonstrations in Qt's demos directory. These are larger and more complicated programs than the Qt Examples and are used to highlight certain features of Qt.
The Qt Widget Gallery also provides overviews of selected Qt widgets in each of the styles used on various supported platforms.
If you are new to Qt, and want to start developing applications, you should probably start by going through the Tutorials.
Mobile Applications
These are demonstrations of some of the capabilities of Qt Quick and Mobility to create feature rich mobile applications.
Guitar Tuner - a guitar tuner made with a QML frontend and a Mobility based backend
Quick Hit - a game that uses multimedia and Qt Quick
Qt Bubble Level - a game that utilizes hardware sensors for effects
QCamera - a camera application that accesses mobile contacts and networking
Painting
Composition Modes demonstrates the range of composition modes available with Qt.
Vector Deformation demonstrates effects that are made possible with a vector-oriented paint engine.
Gradients shows the different types of gradients that are available in Qt.
Path Stroking shows Qt's built-in dash patterns and shows how custom patterns can be used to extend the range of available patterns.
Affine Transformations demonstrates the different affine transformations that can be used to influence painting operations.
Arthur Plugin shows the widgets from the other painting demos packaged as a custom widget plugin for Qt Designer.
Item Views
Interview shows the same model and selection being shared between three different views.
Spreadsheet demonstrates the use of a table view as a spreadsheet, using custom delegates to render each item according to the type of data it contains.
SQL
Books shows how Qt's SQL support and model/view integration enables the user to modify the contents of a database without requiring knowledge of SQL.
SQL Browser demonstrates a console for executing SQL statements on a live database and provides a data browser for interactively visualizing the results.
Rich Text
Text Edit shows Qt's rich text editing features and provides an environment for experimenting with them.
Main Window
Main Window shows Qt's extensive support for main window features, such as tool bars, dock windows, and menus.
Mac Main Window shows how to create main window applications that has the same appearance as other Mac OS X applications.
Graphics View
40000 Chips uses the Graphics View Framework to efficiently display a large number of individual graphical items on a scrolling canvas and highlighting features including rotation, zooming, level of detail control, and item selection.
Embedded Dialogs showcases Qt 4.4's Widgets on the Canvas feature by embedding several fully-functional dialogs in a scene.
Web Browser demonstrates how Qt's QtWebKit module can be used to implement a small Web browser.
Phonon
Media Player demonstrates how the Phonon module can be used to implement a basic media player application.
Note: The Phonon demos are currently not available for the MinGW platform.
Multimedia
Spectrum Analyzer demonstrates how the QtMultimedia Module can be used to capture and play back an audio stream, at the same time allowing the application to access the raw audio data. This application analyzes the audio stream in order to display a frequency spectrum.