A communication platform is described that supports the fast implementation of networked multimedia applications with conference character and collaboration features. The platform exhibits the notion of a site as one of its main abstractions. A site is a collection of workstations, media input, and output devices that are, in terms of control, tightly coupled. Connection and application control is centralized within one site, but distributed among different sites. The platform exports a programming interface with high-level abstractions for session and connection control, allowing application developers to concentrate on scenario and user interface design. The platform was implemented in the course of the European Beteus (Broadband Exchange for Trans-European Usage) project. A tele-meeting application and a tele-teaching application were developed on top of it. Platform components and applications were tested on the European asynchronous transfer mode (ATM) pilot network over a period of nine months. The paper first describes platform architecture and programming interface, then talks about the implementation of platform and applications and their deployment in the harsh environment of a trans-national broadband pilot network.