In this paper we describe the MIThril 2003 wearable computing research platform. MIThril 2003 is a proven, accessible architecture that combines inexpensive, commodity hardware, a flexible sensor/peripheral interconnection bus, and a powerful, light-weight distributed sensing, classification, and inter-process communications software layer to facilitate the development of distributed real-time multimodal and context-aware applications. MIThril 2003 extends the previous MIThril modular architecture into the domain of large-scale wireless group applications by leveraging the availability of inexpensive Linux-based PDA hardware combined with innovative open-source software and custom sensor hardware. We demonstrate the power and functionality of MIThril 2003 by describing compelling real-world wearable research applications created using MIThril 2003 technology.