Winux Operating System by Linuxfx
Real-Time Event Frameworks based on active objects & state machines
A microkernel-based multiserver operating system written from scratch.
Free real-time operating system designed for microcontrollers
Open-source RTOS and Embedded Systems Toolkit for C++ and C
A Debug style tool for OS Free systems
Wayland/QtQuick based OS with incremental updates and bundles
Android, DOS, FirefoxOS, Linux, MacOS and Windows all in one..
SuperWikia: The Runtime/Realtime Environment for Codesmiths
Universal Operating System