I will probably have quite a few posts related to RTEMS, so I thought an introduction would be appropriate. I've been doing a lot of work recently on a project with Eugen, a fellow Ph.D. student, to port the RTEMS Operating System (related blog) to the UltraSPARC T1 Niagara, a 64-bit SPARC-v9 processor.
RTEMS is a real-time operating system (RTOS), which means that its operations can be precisely and accurately timed and that it supports applications that have strict timing requirements. Classes of such applications range from control systems to streaming data processors. Examples that we see (or don't see) everyday are embedded in such things as planes, trains, and automobiles, or multimedia video and audio devices.
RTEMS is notable for a few reasons. First, it's free and open source. Second, it supports a large number of target architectures (platforms). Third, it is in space! Some of the platforms that RTEMS supports are radiation-hardened for outer space, and it is on some of the NASA and ESA equipment floating around up there.
But I don't plan to be a rocket scientist. My interest in RTEMS is for its support of a variety of computer architectures, including the SPARC-v8 architecture. Eugen and I have identified the Niagara as a promising architecture with which to continue our current research direction, and we wanted to have a low-level OS that is small enough to understand. Thus we chose RTEMS and started porting the existing support for SPARC-v8 to the newer SPARC-v9. This has been an ongoing effort for awhile, but we have made quite a bit of success, and hope to contribute our work back to the RTEMS community.
If you want more info about RTEMS, check out its website, which is newly updated.