Apache NuttX
A real-time operating system for embedded systems, scaling from 8-bit to 64-bit microcontrollers with POSIX and ANSI standards compliance.
Apache NuttX is a real-time operating system built for small, deeply embedded systems, scaling from 8-bit to 64-bit microcontroller environments. It emphasizes standards compliance, following POSIX and ANSI standards, and adopts additional APIs from Unix and other real-time operating systems where the standards do not cover embedded-specific needs.
It includes its own simulator so it can be tried without physical hardware, and supports a wide variety of boards and platforms. The project provides getting-started and contribution documentation covering git usage, coding standards, and workflow, and is licensed under Apache 2.0 or a compatible license.