NewOS  
   Loosely based on concepts in BeOS, FreeBSD, NT, Solaris, other modern OSs; goals: be as modern and complete as possible, emphasize platform portability; runs on x86 1, 2/4 SMP CPUs, Sega Dreamcast Hitachi SH-4. Kernel used in OpenBeOS. [Open Source, BSD]
   http://newos.sourceforge.net/

Moo32  
   Early development microkernel.
   http://www.geocities.com/SiliconValley/Vista/7477/os.html

Apostle  
   Free microkernel operating system for i386 architecture, built on Gemini Nucleus, coded in C. Seeks to provide well-designed alternate to extant OSs; goal: create an OS that works because it is appropriate and effective for its users. [open source, GPL]
   http://apostle.sourceforge.net/

Gemini Nucleus  
   Open source project to make a production quality micro kernel based on the latest findings in OS research.
   http://gemini.sourceforge.net/

ReactOS  
   Opensource effort to develop a quality operating system compatible with Windows NT applications and drivers.
   http://www.reactos.com/

Mika OS  
   Low-level coded, AI oriented microkernel OS, based on neural nets. Goal: provide a hight flexible OS architecture based on neural networks and sensor equipped devices. Mach4/Flux-based. [Open Source, GPL]
   http://mikaos.ifrance.com/mikaos/

sMultiTA  
   World's smallest, but full functioning, software extension for MultiTAsking. Very small 200 lines, coded in C, simple, no interrupts or blocking, for hard realtime use; portable, easy to reconfigure to other systems. [Open Source, GPL]
   http://www.dobit.com/emblin/smultita.htm

JTMOS  
   Operating system aimed at OS developers and users who are very advanced at using computers generally; microkernel, multitasking, multithreaded, some garbage collection. [Open Source]
   http://www.fortunecity.com/tattooine/obiwan/32/

LinksOS  
   To be fast, secure, straightforward, fill gap between OS X, Linux, Windows, built on microkernel, coded in Assembly, C/C++; for desktops, workstations, small servers. Description, mail list, OS design documents, CVS, downloads. [Open Source, BSD]
   http://sourceforge.net/projects/linksos/

Spoon Microkernel  
   Hobby and education OS, for Intel compatible CPUs; simple, available source code make it a useful source of learning material. South Africa. Descriptions, documents, screenshots, tips, links. [Open Source, BSD]
   http://www.djm.co.za/spoon/

Programmers Operating SYStem: POSYS  
   To be simple 32-bit multitasking microkernel using all security features of x86 processors, able to load and execute modules for: MS Win32 (32-bit PE, EXE; dynamic link libraries, DLLs), Linux (ELF, a.out). [Open Source, GPL]
   http://posysos.sourceforge.net/