HelenOS is an open-source microkernel-based multiserver operating system written from scratch. It runs on several different CPU architectures (IA-32, x86-64, SPARC V9, IA-64, PowerPC, ARM, MIPS). HelenOS prides in portability, modularity, clean design and coding style.

It does not mimic any existing system and it is not meant to be POSIX-compliant or UNIX-like at all. Just as an example, HelenOS does not support fork().

ChibiOS/RT is a complete, portable, open source, compact and extremely fast RTOS (Real-Time Operating System). You may start reading this introduction.

Quick notes regarding NIX system software issues, references to related work, ideas for future work, and any interesting result along the way. See the nix OS web site http://lsub.org/ls/nix.html

SV is running the incompatible timesharing system (ITS) on a KLH10 -- an emulated KS10 written in C and being executed by an AMD P6-600 running FreeBSD.

Another open-source RTOS. Unlike others, it comes with a task state diagram.

A Linux distribution for small devices, with grapics based on OpenGL, but without using X11.

Another successor to EROS, a capability-based operating system. Attempts to use formal verification.

An introductory text to (using) operating systems, using Plan 9. It is the first draft produced (announced on comp.os.plan9 on 2006-08-31)

A large collection about Unix history, people, etc.

MINIX 3 is a new open-source operating system designed to be highly reliable, flexible, and secure. It is loosely based somewhat on previous versions of MINIX, but is fundamentally different in many key ways. MINIX 1 and 2 were intended as teaching tools;