The source for the Linux kernel used in Windows Subsystem for Linux 2
Hobby operating system, bootloader, kernel, drivers, C library
A BSD-based OS project that aims to provide an experience with MacOS
NVIDIA Linux open GPU kernel module source
Real-Time Event Frameworks based on active objects & state machines
Software development for 4Mb portable, using Z80 CPU and AA batteries
A microkernel-based multiserver operating system written from scratch.
Latest Android builds from PixelBoot.
Casper-fs is a Custom LKM generator to protect and hide files.
The classic RPL programming language reimplemented and reimagined.
Simplest kernel for cooperative multithreading
An little operating system
The first OpenSolaris based distro (since June 2005)
OS bootable from Linux,Windows and others partitions as auxiliary OS
UNIX/LINUX and legal homebrew software on the xbox360 gaming console
Open-source RTOS and Embedded Systems Toolkit for C++ and C
PRTOS is a simple, compact preemptive RTOS for embedded systems
Rewrite Minix 3 from C to D
ext2/3/4 library for microcontrollers
A UNIX-like kernel for the i386 architecture
Mulithreading Arduno library
Run Linux on Windows or other OSes, natively.