The Zephyr OS is based on a small-footprint kernel designed for use on resource-constrained and embedded systems: from simple embedded environmental sensors and LED wearables to sophisticated embedded controllers, smart watches, and IoT wireless applications.
ChibiOS/RT is a compact and fast RTOS designed for embedded applications. It offers threads, mutexes, semaphores, messages, events, timers, flexible I/O with timeout capability. ARM7, Cortex-M3, AVR, MSP430 and x86 are currently supported.
OpenBLT is mostly used as an STM32 bootloader, due to the popularity of STM32 microcontrollers. However, the bootloader’s architecture is such that it can work with any microcontroller and use any type of communication interface to perform firmware updates.
QP is a family of lightweight software frameworks for building responsive and modular real-time embedded applications as systems of cooperating, event-driven active objects (actors). The QP family consists of QP/C, QP/C++, and QP-nano frameworks, which are all strictly quality controlled, superbly
... [More] documented, and commercially licensable.
The behavior of active objects is specified in QP by means of hierarchical state machines (UML statecharts). The frameworks support manual coding of UML state machines in C or C++ as well as automatic code generation by means of the free QM modeling tool.
See also http://sourceforge.net/projects/qpc [Less]