Prex
- Portable, small, realtime microkernel 32-bit OS for embedded systems, coded in C, POSIX emulation layer. Open source, BSD.
- http://prex.sourceforge.net/

PikeOS
- Uses virtualization to protect software investment long-term; implements multiple software partitions on one CPU, strictly separated, each partition can run full OS such as Linux, POSIX, OSEK, or programs. Sysgo AG; Mainz, Germany.
- http://www.sysgo.com/products/pikeos-technology/

Phoenix-RTOS
- Growing article, with links to many related topics. Wikipedia.
- http://en.wikipedia.org/wiki/Phoenix-RTOS

ERIKA Enterprise
- Embedded RTOS for single and multi-core uses, small size, supports advanced scheduling mechanisms for stack size reduction on multiprocessor chip systems. Commercial. Evidence S.r.l.
- http://www.evidence.eu.com/content/view/24/45/

Spring Operating System
- Growing article, with links to many related topics. Wikipedia.
- http://en.wikipedia.org/wiki/Spring_(operating_system)

An Overview of the Spring System
- Description of realtime microkernel and integrated environment, designed and implemented to support/provide predictability, guarantees (on-line dynamic, atomic), end-to-end scheduling, resource reservations; supports call/task admission model; and multipr
- http://research.sun.com/features/tenyears/volcd/papers/mitchell.htm

Real-Time Mach NTT
- Another version of Real-Time Mach, by NTT Laboratories. Contains RT-Mach kernel, FreeBSD 2.2.8 server, real-time shell, RT-Java, Hurd loader. Site has fine 'Getting Started' section: readme, release notes, installation, hardware, compatibility, troubles Q
- http://info.isl.ntt.co.jp/rtmach/

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. [Open Source, GPL]
- http://rtmk.sourceforge.net/

Sphere SP
- A modular RTOS suitable for embedded systems, scalable from tiny stand-alone microkernel up to full client/server OS, supports different processors.
- http://www.miray.de/products/spheresp.html

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/