.QTZ File Extension
What is a QTZ file?
Animation created with Quartz Composer, a development tool created by Apple for processing and rendering graphical data; may include 2D images, 3D objects, textures, audio, MIDI data, and 2D and 3D effects.
QTZ files are used for certain Mac OS X screen savers, such as RSS Visualizer.qtz and Spectrum.qtz. These screen savers are saved in the /System/Library/Screen Savers/ directory.
Quartz Composer is installed with Apple's Developer Tools and is saved in the /Developer/Applications/ directory.