Mobile ad-hoc networks allow wireless devices to freely communicate without the need of any fixed infrastructure. Although many of the emerging applications share the need for multicast communication, their requirements regarding reliable data delivery strongly differ. One single multicast service will thus not provide an acceptable solution for different application and network scenarios. Instead, a multicast service's flexibility and adaptivity is required in both respects, in order to yield good performance. In this context, application-layer multicast services appear promising: As they rely on so-called overlay networks for data dissemination, they do not require network-wide support and can thus easily be optimized for specific scenarios. We in this contribution propose a novel architecture for the flexible composition of scalable application-layer multicast services. To do so, we subdivide the latter into different modules, such as transport and overlay routing. By making modules arbitrarily interchangeable, we increase a service's adaptability and facilitate its development. The service's scalability is generically ensured, by including our approved technique of Local Broadcast Clustering, which is applicable to arbitrary overlay-multicast algorithms, inside the architecture. As we additionally abstract from a specific network access, developed services can easily be operated and evaluated on top of different network technologies, comprising event-based network simulation software as well as true WLAN-capable devices.