Agnix is a small, educational operating system kernel for i386, supporting 32-bit protected memory mode, paging, hardware switched tasks, memory tests, PCI bus, devices, PCI IRQ routing, RT timers, network protocols. It is available with all the source code and is fully compatible with the Linux kernel API.
Alpaca is a multitasking operating system for Z-80 based arcade hardware. It has been designed to run on both Pac-Man and Pengo based arcade machines, but can easily be ported to other machines with similar architectures. It supports four concurrently running processes, task switching, simple inter-process messaging, semaphores, and a basic window-based graphical interface.
DragonFly belongs to the same class of operating systems as other BSD-derived systems and Linux. It is based on the same Unix ideals and APIs and shares ancestor code with other BSD operating systems. DragonFly is differentiated from other operating systems in its class by, among others, the HAMMER file system, Virtual Kernels, swapcache, and the pervasive use of soft token locks. DragonFly provides an opportunity for the BSD base to grow in an entirely different direction from the ones taken in the FreeBSD, NetBSD, and OpenBSD series.
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 FOLK project aims to provide a single patch which incorporates as many Linux kernel projects as can be crammed in. Its goal is to allow people who are interested in experimenting with the different projects to get on with the experimenting, rather than spend time fixing clashing diffs. It also has the goal of giving some of the more obscure projects a better chance of being seen and used. It is not intended for "general use". If a given release is stable, that will be by sheer luck. These are experimental projects, of unknown quality and completeness, being thrown together in ways that the developers are unlikely to have even remotely considered.
GeekOS is a tiny operating system kernel for x86 PCs. Its goal is to be simple enough for beginners to understand and modify, but realistic enough to be interesting and fun. The primary development environment for GeekOS is Linux or Windows using gcc, nasm, and the Bochs PC emulator.