GenApp is a universal and extensible tool for rapid deployment of applications. GenApp builds fully functioning science gateways and standalone GUI applications from collections of de.nition .les and libraries of code fragments. Among the main features are the minimal technical expertise requirement for the end user and an open-end design ensuring sustainability of generated applications. Because of the conceptual simplicity of use, GenApp is ideally suited to scientists who are not professional developers, to disseminate their theoretical and experimental expertise as embodied in their code to their communities by rapidly deploying advanced applications. GenApp has an open extensible resource execution model. To support efficient elastic cloud computing on NSF Jetstream, GenApp has recently integrated OpenStack as a target resource with optional jobspeci .c XSEDE project accounting.