The SpaceDev MMB-100 spacecraft platform is a single-string 100-kg class microsat that is suitable for experiments, flight demonstrations, and highly-responsive missions. It is designed specifically for 1-2 year LEO missions. It has flexible launch options, including the ESPA ring and the SpaceX Falcon launch vehicle. The MMB-100 makes extensive use of commercial off-the-shelf (COTS) parts and software, which enables low cost and rapid development times. Attitude control performance is better than 25 microradians (1-sigma). The power subsystem is flexible, and can accommodate orbit-average payload loads of up to 150 W. Telemetry and data transfers from the spacecraft to the ground are implemented via FTP using standard Internet protocols. The MMB-100 represents a significant departure from conventional spacecraft design practices, and will enable a new generation of small, low-cost satellites.