CindyJS --- mathematical visualization on modern devices --- Visualization and real-time interactive simulation play an important role both in mathematical research and in mathematical communication. The CindyJS Project aims at the development of a software platform and its mathematical foundation that allows a versatile and fast prototyping of mathematical experiments and visualizations which can be used for research and demonstration. The project attacks both the mathematical and the software related aspects of such a platform. In particular, the system should be usable as a flexible authoring system for providing mathematical content that can run in contemporary web browsers, taking advantage of modern hardware and software technologies. Within the CindyJS project a special emphasis (on the mathematical side) is laid on the creation of a system that provides a high mathematical consistency and expressiveness. Another focus (on the computer science side) is to provide an intuitive authoring system that can in particular be used for the creation of web based demonstrations and microlaboratories that run within a browser and on mobile devices. The system, among other aims, should provide easy access to an interactive geometry viewing environment (2D and 3D), to a versatile scripting language and to a reliable physics simulation engine.