The ultra-sensitive accelerometer, developed for NASA to monitor the microgravity environments of Space Shuttle, free orbitors and Space Station, needed to measure accelerations up to 10 mg with an absolute accuracy of 10 nano-g for at least two orbits to resolve accelerations associated with orbital drag. Also, the accelerometers needed to have less than 10-9 F.S. off-axis sensitivity; to be thermally and magnetically inert; to be immune to quiescent shock, and to have an in-situ calibration capability. The utilization of these accelerometers in multi-axis compact seismometers designs that have twelve decades of dynamic range, density profilometers, precision gradiometers, gyros and vibration isolation designs and applications will be discussed. FInally, examples of the versatility of the proof mass suspension system will be demonstrated through the transformation of the basic accelerometer into sensitive anemometers and imaging spectrometers.