By 1995, they knew their customers needed standardized runtime support that integrated completely with the GNU gcc compiler, gdb debugger and tools on the host. As with gcc, portability was a key ingredient, as it had to be available for a wide range of architectures and evaluation boards. In moving into the RTOS business, Cygnus had to consider its own strengths and weaknesses. At least, that's what many people would like to think. Actually, an RTOS, like a restaurant, is a truly good way to go broke fast, unless you know exactly what you are doing.
Many products actually come quite close.
Typically, the user has access to the source but the vendor owns it, and you don't see the source until after you buy the product. Part of the purchase is a non-disclosure agreement, which prevents you from trading improvements with other users of the same product. These constraints are anathema to the open-source model. A number of Linux variants offer real-time capabilities, all of which are open source. Probably the best-known is Victor Yodaiken's RTLinux.