Realtime

Pumpkin, Inc. - Makes Salvo RTOS, designed expressly for very low cost embedded systems with highly limited ROM and RAM (normal uses: 1-2K ROM, 50-100 bytes RAM) and/or no software stack. Priority-based, cooperative multitasking, event services, real-time delays.
http://www.pumpkininc.com/

Enea Embedded Technology - Develops and distributes the OSE family of real-time operating systems and embedded development tools for high reliability telecom/datacom, medical, automotive and safety critical applications.
http://www.enea.com/

Fusion RTOS - A fast (190 cycle context switch), small (1-1.5 K), designed and optimized for next generation DSP systems; and Fusion Net (TCP/IP Stack), Fusion Web (services); all support priority based, realtime, preemptive, multitasking. By DSPOS, Inc.
http://www.dspos.com/DSPOSWeb/rtos/fusion_RTOS.htm

NewMonics, Inc. - Leading supplier of Java-compliant virtual machines for embedded and real-time systems.
http://www.newmonics.com/

Wind River Systems, Inc. - Makes pSOSystem, OSEKWorks, Virtuoso, VxWorks RTOSs (and BSD/OS). Merged with Integrated Systems, Inc., world leader in providing full embedded system software and design automation solutions: software, hardware, custom design, world-class support.
http://www.windriver.com/

Segger Microcontroller Systeme GmbH - Makes, sells, supports embOS RTOS for embedded uses, multitasking, minimum cost, no royalty, fully interruptible, efficient for time critical uses, RAM and ROM needs so small it fits 1-chip uses, leaving more room for user programs.
http://www.segger.com/embos.html

NexGen Software - French software house that designs and markets an Open Embedded TCP/IP suite designed for demanding embedded applications: TCP, HTTP, PPP, VoIP.
http://www.nexgen-software.fr/

REACT - Hard realtime extension, under 30µs interrupt response times; for Linux, and standard with SGI IRIX Unix OS; Silicon Graphics, Inc. Open source.
http://www.sgi.com/products/software/react/

JMI Software Systems, Inc. - Makes C Executive and PSX multitasking, ROMable kernels for embedded systems. C Ex runs on 8/16/32 bit CISC CPUs, many RISC CPUs, DSPs, over 20 so far: fast context switch, compact. Options: DOS file system, TCP/IP, SNMP. PSX is medium-size kernel, between small basic kernels and full Unix; optional subset of POSIX.1 system calls.
http://www.jmi.com/

AI Lab Zurich: Links: Embedded and Real-Time Systems - Medium-size link page; several categories.
http://www.ifi.unizh.ch/groups/ailab/links/embedded.html

CMX Company - Makes multitasking RTOS products: CMX-RTX (full RTOS), CMX-TINY+ (small RTOS), CMX-TCP/IP, CMXBug, CMXTracker. These support most 8/16/32/64-bit embedded controllers, processors, DSPs, over 30 compiler vendors.
http://www.cmx.com/

C Kernel - Realtime preemptive kernel coded fully in C, so is highly portable to different hardware platforms and easily embeddable; Descriptions, full source code, examples, C Style Guide and programming Guidelines. [Free]
http://home.hetnet.nl/~p_vd_vlugt/

Micro Digital, Inc. - Makes SMX: no-royalty, modular, preemptive multitasking, small fast, many featured RTOS for embedded systems. Portable to all 32-bit processors, now on ARM, ColdFire, PowerPC, SH3/4, x86. Unlike generic C kernels, it exploits strengths of x86 to make it easier to program.
http://www.smxrtos.com/

VenturCom, Inc. - Enabling Windows NT and Windows CE for embedded and real-time applications
http://www.vci.com

Xpolyplus - Realtime OS and development system for programs for industrial automation, telecontrol, machine automation. It is C-Scada: does all functions of SCADA, plus control (more so with neXor I/O hardware); by XPLAB. English, Italian.
http://www.xpolyplus.com/

Jaluna OSware - Virtualization platform that allows embedded products to run heterogeneous operating systems and applications.
http://www.jaluna.com/

TurboTask RTOS - For Z80 and Z180 compatible processors; full-featured, tiny, size ranges from 1k to 2.5k, set by features used; written in pure Assembly, making it maximally small, fast; no royalty; low cost licenses for binary and full source code. By Softools, Inc.
http://www.softools.com/turbotask.htm

Kadak Products Ltd. - Makes AMX RTOS, KwikNet TCP/IP stack and Web server, KwikLook fault finder, KwikPeg GUI with graphics library. A high quality realtime software foundation for embedded products.
http://www.kadak.com/

Folsena Microsystems - Makes Mavos preemptive, realtime micro (compact) OS; highly portable, is all one needs to run native and J2ME CLDC Java (VM) programs on embedded or wireless systems.
http://folsena.com/

Quadros Systems, Inc. - Makes RTXC 3.2 and RTXC Quadros, for convergent processing in embedded uses. Seamless use with microprocessors, DSPs. Configurations: single stack, dual stack, multi stack; multicore, multiprocessing.
http://www.quadros.com/

SCIOPTA RTOS - Assembly coded high performance kernels, internet protocols (TCP/IP), filesystem, support for distributed systems, DRUID system level debugger. Supports most 32-bit processors; COMPACT is for 8/16-bit controllers. By Litronic AG.
http://www.sciopta.com/

TenAsys Corp. - Makes iRMX family of RTOSs, designed and optimized for reliable, RT applications for x86 processor-based systems: PC-compatibles, and Microsoft Windows software; embedded, Multibus and Multibus II computers.
http://www.tenasys.com/

Tics Realtime - Modern message-based architecture. Introduced June 1992, many uses: cell phones, small handheld devices, large factory automation systems, Space Shuttle.
http://www.concentric.net/~Tics/

VITA - The VMEbus International Trade Association
http://www.vita.com

Realtime Operating System - Growing article, with links to many related topics. Wikipedia.
http://en.wikipedia.org/wiki/Real-time_operating_system

CsLEOS - A RTOS for high safety systems, brick-wall time, space partitioning of separate loaded programs with different levels of criticality, for greatly reduced test, certification costs, compliant to ARINC653 open system interface definition. By BAE Systems North America.
http://platformsolutions.na.baesystems.com:8080/CsLeos/

On Time Informatik GmbH - Makes RTOS-32, and realtime multitasking development tools, for x86-based embedded systems; no royalty, full source code available on all products. Supports Borland, Microsoft, Watcom C/C++ compilers; DOS, Win32 compatible API gives easy ports of extant programs.
http://www.on-time.com/

SW Datentechnik GmbH - Realtime software, hardware, services: QNX, SQL, multiplatform RAD, portable UNIX-Windows, networking, RAID, multiport.
http://www.swd.de