As described on the GammaRay project site, "GammaRay is a tool for examining the internals of a Qt application and to some extent also manipulate it. GammaRay uses injection methods to hook into an application at runtime and provide access to a wide variety of interesting information. It provides easy ways of navigating through the complex internal structures you find in some Qt frameworks, such as QGraphicsView, model/view, QTextDocument, state machines and more."
GammaRay can be used as a high-level debugger in an easy way with its QObject introspection tools and ability to handle complex Qt frameworks, among other purposes for this open-source application.
GammaRay 1.1 was released this week and new to this version is a plug-in system for tools, a graphical state machine viewer, object hierarchy visualization, new widget export abilities, an improved widget tree model, and various other enhancements. There's also MingW support should you be after GammaRay on Microsoft Windows.
The release announcement for GammaRay 1.1 with source links can be found on the KDE development list. The GPL code itself is developed on GitHub.