OCEOS is a real-time pre-emptive fixed priority operating system that can be used in applications that require European Cooperation for Space Standardization Category B or ISO 26262 standards. It has a small memory footprint (<10 kBytes), requires only one system stack rather than a stack for each task, and provides support for precisely timed data outputs independent of task scheduling. It is available initially for applications running on SPARC based hardware with ARM release early in 2021. The support of the European Space Agency in developing OCEOS is acknowledged.