Famous pioneering microkernel research OS, from Carnegie Mellon University: CMU. It lead to many well known OSs: NeXT, Flux (part of the Flux-Fluke-Flask progression, though Fluke is new code, and which is viewed by many as the follow-on to Mach), GNU Hurd.
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 continuously in the presence of faults.
By Real-Time and Multimedia Laboratory, Department of Computer Science, Carnegie Mellon University. RT-Mach is a resource kernel, a kernel provides resource-centric services, which can then be used to satisfy end-to-end QoS needs.