We present Epic, an open mote platform for application-driven design.??Sensornet platforms, like most embedded systems, are tightly coupled to their applications.??This coupling can make it difficult for general-purpose platforms to address application-specific needs, forcing platform designers to repeatedly reimplement functionality.??Inspired by the hierarchical nature of software and integrated circuit design, we propose sensornet platforms be composed hierarchically from a family of modular components.??This approach makes platform development accessible to a much wider community; developers do not need to be analog, sensor, or radio frequency experts, and can instead reuse components that encapsulate the needed functionality.