Application Service Providers (ASPs) are changing the way software is being used and distributed. Using ASP technology, users do not have to own software anymore, nor do they have to install it on their local computing environment to use it. Instead, the software is installed by the ASP on some remote server that also performs the necessary data management. Customers use the software via the Internet and pay a usage fee, where applicable. Our longer-term vision is an open ASP marketplace where anybody can offer their software modules with little technical and administrational overhead. This paper presents an XML/XSL-based approach to support this paradigm. In order to make software available for ASP-style execution, providers only need to write a simple XML wrapper that states the location and the input/output specifications of the module. We also propose a new XSL command to control software execution and we discuss its possible integration into the current XSL standard.