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.org/

rtmk
- Realtime microkernel: preemptive, fully re-entrant, multithreaded, SMP, continuations, full locking primitives; shares many ideas with Mach, developed by CMU in late 1980's, early 1990's, stopped in 1994. [GPL]
- http://rtmk.sourceforge.net/

E.R.I.K.A.
- Microkernel RTOSs and set of integrated tools to develop embedded realtime applications, made to support all architectures used in power train controllers in automotive industry. Kernels have 2 main layers: Kernel Layer, Hardware Abstraction Layer, HAL. [
- http://erika.sssup.it/

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/

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/

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

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/

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

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

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/