1. A system responsive to a user generated natural language speech utterance, comprising: an agent architecture that includes a plurality of domain agents, each of the plurality of domain agents being an autonomous executable configured to receive, process, and respond to requests associated with a respective context; a parser configured to determine a context for one or more keywords contained in the utterance and to determine a meaning of the utterance based on the determined context, wherein the parser selects at least one of the plurality of domain agents based on the determined meaning, wherein the selected domain agent is configured to receive, process, and respond to requests associated with the determined context; an event manager configured to coordinate interaction between the parser and the agent architecture; and an update manager that enables the user to purchase one or more domain agents from a third party on a one-time or subscription basis.