Buenos is a small SMP operating system skeleton that can be used as a base for operating systems project courses. The system is intended to be used as OS project base code which students can improve. Extensive documentation with suggestions for assignments or exercises is included with the system. It runs in a machine simulator called YAMS, which is its sister project.
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.
Haiku (formerly known as OpenBeOS) is an operating system designed from the ground up for desktop computing. Inspired by the BeOS, it aims to provide users of all levels with a personal computing experience that is simple yet powerful, and free of any unnecessary complexities. It aims for source and binary compatibility with BeOS R5.
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.
JTMOS stands for "Jari Tuominen's Minimal Operating System". The JTMOS operating system project aims to create a fully functional multitasking x86 operating system. It primarily targets low-end systems with small hard disks, preferably i586 family or newer. Currently focus in the project is on communication, TCP/IP stack, and building up FAT file system support. JTMOS mimics some features from Linux-style operating systems like the root directory system. JTMOS can already boot up from DOS, or independently from hard disk or floppy disk with its own custom bootloader.
MikeOS is an operating system for x86 PCs, written in assembly language. It is a learning tool to show how simple OSes work, with well-commented code and extensive documentation. It features a text-mode dialog-driven user interface, a file manager and machine code monitor, and over 60 system calls for use by third-party programs.
MirBSD originated as a patch set against OpenBSD-current, an ultra secure operating system and NetBSD derivate, and has since also incorporated changes from NetBSD, a 4.4BSD-derived ultra portable operating system. It features bugfixes, code removal for the sake of simplicity, and feature enhancements over stock OpenBSD as well as a much more up-to-date GNU toolchain, careful integration of patches from other projects (such as KAME), and many improvements. It works on the Intel Pentium and some 80486 machines with more than 32 MiB RAM and the SPARC, and a port to the PowerPC Macintosh is in preparation.