Azure Sphere is a secured, high-level application platform with built-in communication and security features for internet-connected devices.
It comprises a secured, connected, crossover microcontroller unit (MCU), a custom high-level Linux-based operating system (OS), and a cloud-based security service that provides continuous, renewable security.
For more details see https://docs.microsoft.com/en-us/azure-sphere/product-overview/what-is-azure-sphere