The DUP System is a language for productive, parallel, and distributed stream processing on POSIX systems. Programming with DUP is similar to writing shell scripts with pipes except that filters can have multiple inputs and outputs. Furthermore, the computation can be spread across multiple computers. A distinguishing characteristic of DUP compared to other streaming languages is that filters can be written in almost any programming language. The DUP System distribution includes the runtime system and a collection of over a dozen multi-stream filters.