Wikipedia
ChorusOS is a microkernel real-time operating system designed as a message-based computational model. ChorusOS started as the Chorus distributed real-time operating system research project at Institut National de Recherche en Informatique et Automatique (INRIA) in France in 1979. During the 1980s, Chorus was one of two earliest microkernels (the other being Mach) and was developed commercially by Chorus Systèmes. Over time, development effort shifted away from distribution aspects to real-time for embedded systems.
Sun Microsystems acquired Chorus Systèmes, in 1997. Sun (and henceforth Oracle) no longer supports ChorusOS. The founders of Chorus Systèmes started a new company called Jaluna in August 2002. Jaluna has subsequently become VirtualLogix. VirtualLogix was itself acquired by Red Bend in September 2010. VirtualLogix designed embedded systems using Linux and ChorusOS (which they called "VirtualLogix C5"). C5 was described by them as a carrier-grade operating system, and was actively maintained by them. The Red Bend web site shows no trace of current activity around the ChorusOS/VirtualLogix C5 microkernel. The source repository on SourceForge also shows zero sign of activity since July 2007.
The latest source tree of ChorusOS, an evolution of version 5.0, has been open-sourced by Sun and is available at the Sun Download Center. The Jaluna project has completed these sources and the current version the Jaluna-1 software is available at SourceForge. Jaluna-1 is described there as a RT- POSIX layer based on FreeBSD 4.1, and the CDE cross-development environment. This software is still used according to the download server .