In this paper, the authors present a hardware and software platform for wireless sensing applications. The hardware kit consists of two types of self-contained, expandable sensor nodes, as well as, a multipurpose base station and programmer, a cascadable charger and sensor modules. The software kit consists of an Integrated Development Environment (IDE) for application programming and RF (Radio Frequency) debugging utilities on the host computer, plus a lightweight operating system with support for data logging and remote firmware reprogramming. Together, this package facilitates application development of ultra-compact, wearable wireless sensing systems.