1. Plug-in configurable middleware for managing distributed applications, the middleware comprising: at least one core runtime engine capable of a plurality of concurrent instantiations on at least one host, each core runtime engine instance comprising sufficient functionality to support plug-in architecture and each core runtime instance in communication with other concurrent core runtime engine instances; a plurality of personalities, one or more of the plurality of personalities associated with one or more of the plurality of concurrent core runtime engine instances, and each personality comprising a definition of the function of the core runtime engine instance to which that personality is associated; and a plurality of pre-defined plug-ins, each plug-in associated with one or more of the plurality of personalities and comprising runtime code that provides at least a portion of the function of each personality to which the plug-in is associated.