CUMULOS is a tiny three-camera VIS/SWIR/LWIR sensor system flying as a hosted payload on the NASA/JPL ISARA mission, a 3U CubeSat. The CUMULOS sensors provide a small-aperture, large field-of-view, remote sensing payload suitable for testing the performance of passively-cooled commercial sensors for weather and environmental monitoring missions. The CUMULOS consists of a 0.4-0.9 µm visible CMOS camera, a 0.9 -1.7 µm short-wave infrared InGaAs CMOS camera, and a 7.5-13.5 long-wave infrared VOx microbolometer camera. All three cameras and associated electronics fit into less than 1U of spacecraft volume and were accommodated on the ISARA mission on a non-interference basis. CUMULOS is designed for point-and-stare imaging and acquires almost simultaneous 3-band coverage of regions approximately 200 x 150 kilometers in size, at ground sample distances from 130 to 400 meters from an orbital altitude of 450km, 52° inclination. Remote sensing applications being investigated include: hotspot detection (including fires, gas flares, and volcanic activity), detection of nighttime lights, cloud cover detection, surface temperature characterization, and airglow phenomenology. Operational since June 2018, the sensors have taken sample daytime and nighttime cloud imagery including, notably, the detection of airglow-illuminated clouds by the SWIR camera operating in high-sensitivity mode. The LWIR microbolometer camera provides useful single-band cloud and earth surface thermal imagery. The visible camera can provide daytime pictures as well as high-sensitivity nightlights imagery. The combination of all three cameras working together has proven quite successful for characterizing nightlights and thermal hotspots in manner similar to the much larger VIIRS payload that flies on JPSS, and for researching compact sensor nighttime weather imaging possibilities. We present example results on nightlights mapping of urban areas and road networks, detection of gas flares and other industrial heat sources, detection of urban heat islands, and demonstrate how the combination of sensors work together to map light and thermal features of rapidly developing urban areas. CubeSats sensors, such as CUMULOS, can complement existing of larger space sensors, such as VIIRS, by acting as testbeds for new spectral bands, imaging at higher resolutions over smaller fields of view, and flying in different orbits to measure nightlights signatures at different times during the night. The CUMULOS is also an engineering test bed for developing techniques for the calibration of small sensors in space, demonstrating a calibration and georegistration data pipeline, and automating CubeSat remote sensing data collection. These experiences, lessons and procedures will be described as well.