Apache Mynewt

Mynewt entered the Apache Incubator in 2015 and became a top-level project two years later. It targets microcontrollers with a few tens of kilobytes of RAM and ships with the newt build tool, which fetches packages and assembles a firmware image much like a package manager would.

Two of its components travelled further than the OS itself. The NimBLE Bluetooth Low Energy stack is now what ESP-IDF uses on the ESP32, and the MCUboot secure bootloader started life as Mynewt's own before becoming a standalone project that Zephyr uses too. An unusual fate for an RTOS, though not a bad one: to be remembered as a supplier of spare parts.