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] Nilsen Elektronikk AS - Makes 2 very small, open source realtime OSs for embedded systems, written in C: proc Real-Time Kernel, preemptive, mature; nesos Finite State Machine Operating System (FSMOS), modular, use concurrent programming methods in little time and space. Also: nemon Boot and Debug Monitor; Embedded Web Servers. CarbonKernel - RTOS simulator based on event-driven simulation methods with concurrent target debugging abilities, mimics OS behavior, to implement and test embedded software on workstations. Descriptions, downloads, documents. [Savannah, Open Source, GPL] RTMX, Inc. - Makes RTMX O/S: IEEE POSIX realtime extensions to OpenBSD, with vendor specific ports for embedded, dedicated systems, application specific Internet/intranet servers. Many fine features. North Carolina, USA. S.Ha.R.K. - Dynamic configurable kernel architecture to support hard/soft/non realtime use with interchangeable scheduling algorithms: fully modular in scheduling policies, aperiodic servers, concurrency control protocols; all not modular in most traditional OSs. Derived from HARTIK: HArd Real TIme Kernel. [GPL] Linux Journal: Open Source Software for Real-Time Solutions - Compares 2 open source OSs for embedded uses: RTLinux, eCOS by Cygnus. NicheTask - Open source multitasking embedded operating system with a proven track record, expressly designed for embedded devices with limited resources. BeRTOS - A free real time operating system suitable for embedded platforms. Runs on several microprocessors and microcontrollers, ranging from 8 bits to 32 bits and on personal computers. RadiOS - A microkernel based operating system, aims at binary compatibility with QNX Neutrino. RIOT - An operating system for the Internet of Things. Contiki - An open-source operating system for the Internet of Things. It connects tiny low-cost, low-power microcontrollers to the Internet. Atomthreads - A free, lightweight, portable, real-time scheduler for embedded systems.