Linux

Finite State Machine Labs, Inc.: FSMLabs
Makes dual kernel RTLinux and RTCore/BSD, and OpenRTLinux RTOSs, realtime networking, protected memory, XML/RPC controls, embedded Linux developer kit; has RT developer tutorials and white papers; second tier support for Linux product vendors; software development, consulting (embedded, cluster, SMP).
http://www.fsmlabs.com/

KURT: KU Real Time Linux
by University of Kansas (KU) Center for Research, Inc. Between a hard and soft real-time OS.
http://www.ittc.ku.edu/kurt/

LinuxDevices.com: KURT: The KU Real-Time Linux
KURT introduction and analysis.
http://www.linuxdevices.com/cgi-bin/article_view.cgi?artid=AT9514980326

OCERA
Open Components for Embedded Real-time Applications: integrated execution environment for embedded realtime programs. Combines 2 kernels, Linux and RTLinux-GPL to support critical tasks (RTLinux-GPL executive) and soft realtime programs (Linux kernel).
http://www.ocera.org/

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

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

RTAI
RealTime Application Interface for Linux: realtime extension allows writing programs with strict timing constraints for Linux. Supports ARM, PowerPC, x86 32/64.
https://www.rtai.org/

RTAI.dk
Wiki for DIAPM RTAI RealTime extension to Linux; much information, instructions, tips, success stories, related projects, links, bootable CDs.
http://www.rtai.dk/cgi-bin/gratiswiki.pl

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

RTLinux Free
Portal for free version of RTLinux; news, FAQs, search, Forum, downloads, FSMLabs contact; OCERA.
http://www.rtlinuxfree.com/

RTLinux-gpl FTP Repository
FTP and mail list archives, anonymous CVS access.
http://www.rtlinux-gpl.org/

Xenomai
Hard realtime development framework, works with Linux kernel; pervasive, interface-agnostic, support to programs, seamlessly integrates with GNU/Linux environment; based on abstract RTOS core, build any kind of realtime interfaces, over nucleus which exports set of generic RTOS services.
https://gna.org/projects/xenomai/

Xenomai
Wiki for realtime Linux framework: news, information, instructions, tips, success stories, roadmap, links.
http://www.xenomai.org/index.php/Main_Page

Team Takes Different Path to Real-time Linux
RTLinux doesn't try to change Linux into an RTOS, it instead provides a new RT kernel incorporating Linux as a low-priority thread, so the RTOS stays small, streamlined and keeps Linux as a base for common applications. [EE Times] <small>(July 5, 2000)</small>
http://www.eetimes.com/story/OEG20000705S0044

Linux, Real-Time Linux, & IPC
When dealing with realtime systems, IPC overhead becomes important; examines two of the best IPC mechanisms available for Linux: FIFO, shared memory. [Dr. Dobb's Journal] <small>(November, 1999)</small>
http://www.ddj.com/184411098

RTLinux: An Interview with Victor Yodaiken
RTLinux's main architect gives advice for budding computer scientists. [ACM Crossroads] <small>(October, 1999)</small>
http://www.acm.org/crossroads/xrds6-1/yodaiken.html