RT-Thread RTOS is an open source real-time operating system for 16-bit and 32-bit microcontrollers, with components which include a hard real-time kernel, a command line shell, a device virtual file system, and a graphic user interface. RT-Thread RTOS 0.4.x series will be licensed under the Apache License v2.
From the linked article:
Object oriented real-time core (while remaining the elegant and flexible style of C Programming Language);
Object-oriented in C? Elegant in C?
It’s certainly possible, just kind of hard. Look at the Linux kernel’s VFS layer.
C isn’t the most elegant language. Most things are much more elegant in languages like Haskell, Ruby, or Python. However, there are a few cases where the low-level-ness of C allows you to write really elegant code.
Also, I think a lot of elements of C++, especially const-ness, RAII, and references are very elegant.