Concurrent Computer Corp.
   Makes PowerMAX OS: fully preemptive, multi-threaded, Unix-based RTOS. Leading provider of concurrent real-time multiprocessor OSs, high-performance real-time computer systems, solutions, software for business and government. Focus: strategic business area
   http://www.ccur.com/

Maruti
   Goal: create an environment for developing and deploying critical applications with hard real-time constraints in a reactive environment. Such applications must be able to execute on a platform of distributed and heterogeneous resources, and operate conti
   http://www.cs.umd.edu/projects/maruti/

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.
   http://www.rtmx.com/

USIX
   Provides source and binary compatibility with SVR4/386, with: guaranteed response time to interrupts in real-time uses, multiprocessor kernel architecture, better resource utilization, more robust file system, able to dynamically extend kernel with no re-
   http://usix.rosweb.ru/