EROS is the first high-performance capability-based operating system to run on commodity hardware. Everything in the system -- resources, processes, files, and so forth -- is named and protected by capabilities.
EROS is also a persistent system. The entire state of the system -- including processes -- is saved periodically. When the system restarts after a shutdown or a power failure, all processes resume right where they left off. In addition to performance advantages, this makes it easy to build processes that extend the basic facilities of the system.
More information on EROS can be found at the EROS Web Site.
Work is about to begin on the second generation of the EROS system, which will emphasize real-time, multiprocessing, and embedding. This is a great area for undergraduate and masters student research projects.