In March 2004, recognizing the importance of sensor networks, the Chinese Academy of Sciences and the Hong Kong University of Science and Technology launched a joint effort to investigate both fundamental and practical research issues in sensor networks. The goal of this research is to build lightweight optimized sensor systems on a massive scale, namely the BLOSSOMS project. The objective of this research project is to identify research issues at all levels from practical applications down to the design of sensor nodes. This paper reports the status of the project as of April 2005. First, other than making MOTE-compatible sensor nodes, this project has studied the hardware and software co-design and the associated "sensor node on a chip" technology with the aim to make sensor nodes small in size, light in weight, cheap in cost, and low in power consumption. Second, additional toolkits for simulation/emulation and evaluation of sensor networks have been developed to support research at different levels. Third, a number of applications have been investigated and implemented since the launch of this project, and this paper will address two of them. One is an embedded remote health care system based on wireless sensor network technologies to introduce a scalable wireless personal medical network around human?s body. The other is a moving object counting system based on an ultrasonic sensor network, which can be used but not limited to crowd estimation and traffic monitoring and coordination.