MicroC/OS is most often called µC/OS or uC/OS. The second generation version is MicroC/OS-II, µC/OS-II, uC/OS-II. They are low-cost priority-based pre-emptive realtime multitasking operating system (OS) kernels for microprocessors, written mainly in the C programming language. They were originally published in a book by Jean J. Labrosse; µC/OS The Real-Time Kernel, ISBN 0-87930-444-8, which purpose was to describe the internals of a portable OS. It is now a product, maintained by Micrium Inc. Licensing can be per product or product line, with no royalties, or free for non-commercial uses.