The Mozart Programming System is a multiplatform implementation of the Oz programming language, developed by an international group, the Mozart Consortium, which originally consisted of Saarland University, the Swedish Institute of Computer Science, and the Université Catholique de Louvain.

Mozart excels in creating distributed, concurrent applications, because it makes a network fully transparent. It supports GUI applications through Tcl/Tk integration; because it runs applications in a virtual machine, applications can be developed once and run on many different platforms.

The driving goal is to separate the fundamental aspects of programming a distributed system: application functionality, distribution structure, fault tolerance, security, and open computing.

The current Mozart release completely separates application functionality from distribution structure, and provides primitives for fault-tolerance, open computing, and partial support for security.

NEM notes that "QTk" is the name of the Mozart/Oz [L1 ] binding to Tcl/Tk [L2 ].