Gaspard is a visual programming environment devoted to the development and control of scientific parallel applications. par The two paradigms of parallel programming (task and data parallelism) are mixed in Gaspard: a hierarchy of task graphs operates on array flows. These two levels are mixed in a common metaphor. An application is designed as a printed circuit: the programmer specifies tasks as boards or chips and instantiates tasks by plugging them into slots. par The number crunching applications developped using Gaspard are deployed on metacomputing platforms. The visual specification of the application mapping may be dynamically modified at runtime according to the information provided by Gaspard.