These are realtime operating systems (RTOSs) that range from full Unix, and total POSIX compliance, to being less Unix-like, but which are still very POSIX compliant. They are categorized as realtime "Unix-type" OSs instead of realtime "Unix" because some of these OSs are not full Unix, but are extremely, or very, or mostly Unix-like; in other words, some are more Unix-like than others. There is a virtual continuum of OSs from full Unix all the way to those that are merely somewhat POSIX compliant. This category holds those that are most Unix-like and POSIX compliant.