Visopsys is an alternative operating system for PC compatible computers. Under development since late 1997, this system is small, fast, and open source. It features a simple but functional graphical interface, real preemptive multitasking, and virtual memory. Though it attempts to be compatible in a number of ways, Visopsys is not a clone of any other operating system. You can demo the distribution from a "live" CD, USB stick, or floppy disk.
amforth is an extendible command interpreter for the Atmel AVR ATmega microcontroller family. It has a turnkey feature for embedded use as well. It does not depend on a host application. The command language is an almost compatible ANS94 forth with extensions. It needs less than 8KB code memory for the base system. It is written in assembly language and forth itself.
ReactOS is an advanced operating system providing a ground-up implementation of a Microsoft Windows XP/Windows Server 2003-compatible operating system. It aims to achieve complete binary compatibility with both applications and device drivers meant for XP and NT 5.2 operating systems by using a similar architecture and providing a complete and equivalent public interface. Written completely from scratch, ReactOS is not a Linux based system, and shares none of the UNIX architecture.
Fiwix is an operating system kernel based on the Unix architecture and fully focused on being Linux compatible. It is designed exclusively for educational purposes, so the kernel code is kept as simple as possible for the benefit of students. It runs on the 32-bit x86 hardware platform, and is compatible with a good base of existing GNU applications.
The Openwall Linux kernel patch is a collection of security "hardening" features for the Linux kernel. In addition to the new features, some versions of the patch contain various security fixes. The "hardening" features of the patch, while not a complete method of protection, provide an extra layer of security against the easier ways to exploit certain classes of vulnerabilities and/or reduce the impact of those vulnerabilities. The patch can also add a little bit more privacy to the system by restricting access to parts of /proc so that users may not see what others are doing.
HelenOS is a microkernel-based multiserver operating system designed from scratch. By decomposing the operating system functionality into tens of isolated but intensively communicating userspace servers, it provides a computing environment that has several virtues such as flexibility, increased robustness, well defined explicit interfaces, and smaller complexity of individual components. HelenOS does not aim to be another clone of Unix or some other legacy system and is not POSIX-compliant (even though it may seem POSIX-similar at times). Instead, the goal has been to design it according to what is the most elegant and right thing to do. What makes HelenOS unique among the other multiserver operating systems is its multiplatform and multiprocessor microkernel. It will run on seven different processor architectures ranging from a 32-bit uniprocessor little-endian ARMv4 to a 64-bit multicore big-endian UltraSPARC T1.
The Working Overloaded Linux Kernel (WOLK) project provides stable and development kernels for either server or testing purposes. These kernels provide a server kernel and also a service for developers and end users who can't be up-to-date with the latest kernels/patches but want to test new kernel features. Patches may be added upon request.