Many Wireless Sensor Network (WSN) applications are composed of a mixture of deployed devices with varying capabilities, from extremely constrained 8-bit “Motes” to less resource-constrained 32-bit “Microservers”. EmStar is a software environment for developing and deploying complex WSN applications on networks of 32-bit embedded Microserver platforms, and integrating with networks of Motes. EmStar consists of libraries that implement message-passing IPC primitives, tools that support simulation, emulation, and visualization of live systems, both real and simulated, and services that support networking, sensing, and time synchronization. While EmStar’s design has favored ease of use and modularity over efficiency, the resulting increase in overhead has not been an impediment to any of our current projects.