ChibiOS/RT is a free and efficient RTOS designed for deeply embedded applications. It offers a comprehensive set of kernel primitives and supports many architectures: ARM7, Cortex-M0, Cortex-M3, Cortex-M4, PowerPC e200z, STM8, AVR, MSP430, ColdFire, H8S, x86.
32 bit low level Operating System
This site will be a gift to MenuetOS, a 32 bit assembly coded operating system from Finland, Russia and Hungary.
64-BIt Operating System with Compiler
TempleOS is a 64-bit kernel with compiler, graphics library and tools. It is not a Unix. It was made from scratch.
Oberon V4 for Linux and sources for different Oberon V4 implementation
Here you can find both an Oberon V4 system for Linux (x86) as well as a collection of sources for various other platforms. Oberon V4 was implemented at ETH Zurich for several platforms. Binaries can be found on their server and on the one of the University of Linz where Mössenböck's group did further development after he left ETH and the Group at ETH concentrated on System 3. More Information can be found in the wiki https://sourceforge.net/p/oberon/wiki/Home/ of this Project and on Wikipedia https://en.wikipedia.org/wiki/Oberon_(operating_system). In 2013 they were moved here for easy access and, in case of interest, collaboration on further development. The Oberon mailing list is an established channel for its discussion and followed also by the administrators of this SF project.  ftp://ftp.ethoberon.ethz.ch/Oberon/OberonV4/  ftp://oberon.ssw.uni-linz.ac.at/pub/Oberon/  https://lists.inf.ethz.ch/mailman/listinfo/oberon
This project coordinates the efforts of people to port Linux to the Renesas (formerly Hitachi) SuperH family of processors, including the SH-2, SH-3, and SH-4.
LoseThos, a free, 64-bit, multicore, PC operating system designed from scratch -- not a Unix. No bloat. Boots in 2 seconds. Comes with games, C compiler, tools and lots of demos of the API! Test-drive or install -- it is a live CD.
Operating System Framework for a MIPS Simulator. The project includes a multi-threaded MIPS Simulator and a naive Operating System and an Assembler for the simulated architecture, intended to be used for instructional and educational purpose.
This is a collection of libraries contained : Shared memory allocation, configuration script processor, containers (trees, lists, queues, stacks), file system abstraction, network library, timers/threads, Image library, Display libraries, and more.
MkLinux: Linux at Mach 3 MkLinux is a port of Linux to the Mach 3 MicroKernel. Its home page can be found at http://www.mklinux.org and its primary ftp site is ftp://ftp.mklinux.org. This site is for bug tracking & other administrivia.
This project is intended for those who are interested in the workings of simple Operating System. It's made easy to understand. This project is a series of program packages. The packages are progressive... from the simplest to a complete working OS.
Support for non-Linux Unix binaries See also sourceforge.net/projects/linux-abi