Qt is a cross-platform application development framework that can be used to build mobile apps. It was previously bundled with Nokia's Maemo and MeeGo mobile operating systems. Qt allows developers to write once and deploy applications across Android, Symbian, and other platforms through projects like Necessitas and wrappers. Some key advantages of Qt include being based on C++, supporting cross-compilation, having a strong API and documentation, and allowing easy development of graphics-intensive apps through OpenGL ES support.