1. A peer-to-peer network system, comprising: a plurality of peer nodes coupled to a network; a class of software module provided by one or more of the peer nodes; a module class identifier that uniquely identifies the class of software module; one or more module specification advertisements corresponding to the class of software module, wherein each module specification advertisement describes a module specification including an expected on-wire behavior and a protocol of the class of software module; and one or more module implementation advertisements corresponding to each module specification advertisement, wherein each module implementation advertisement describes a particular module implementation of a corresponding module specification, wherein each module implementation is configured to execute within a particular execution environment.