The MANTIS MultimodAl system for NeTworks of In-situ wireless Sensors provides a new multithreaded embedded operating system integrated with a general-purpose single-board hardware platform to enable flexible and rapid prototyping of wireless sensor networks. The key design goals of MANTIS are ease of use, i.e. a small learning curve that encourages novice programmers to rapidly prototype novel sensor networking applications in software and hardware, as well as flexibility, so that expert researchers can leverage or develop advanced software features and hardware extensions to suit the needs of advanced research in wireless sensor networks. Categories and Subject Descriptors D.4.7 [Operating Systems]: Organization and Design - real-time systems and embedded systems, interactive systems. C.3 [Computer Systems Organization] Special-purpose and Application-based Systems - real-time and embedded systems. General Terms Design, Experimentation, Performance, Security, Human Factors. Keywords...