This paper deals with free software and open source development projects, ie with the emergence of a form of noncommercial production of the software. Without payment nor important financial investment, without planification nor prior design, complex products as Linux or Apache could be born. All occurs as if they emerged from a kind of « magic cauldron » (Raymond, 1999). We try to understand and to clear up the mysteries of this « cauldron ». The production engineering constraints and the cycle of development and life of software are studied in the light of existing institutional framework (the copyright or open sources licences like GPL). The structures of organization and coordination of the open source projects rest then on the modulari...