The operating system (OS) running on a wide range of internet of things (IoT) devices, such as sensors, home appliances, industrial gateways, and edge devices, is a fundamental building block of the IoT software stack. To accelerate their firms' digital transformation, enterprise architecture (EA) pros must have a holistic view of IoT device OSes. This report analyzes the strategic benefits and typical architecture of an IoT device OS, defines market segments, and presents representative open source and commercial offerings in each segment for architectural consideration.