Micrium’s uC/OS-III real-time kernel is now officially source available. As a result, developers, researchers, and students can download uC/OS-III’s source code free of charge. Micrium is also making several PDF versions of the uC/OS-III, The Real-Time Kernel book available for free download. Each version is tailored to a different embedded platform.
According to Micrium, the source-available model combines the best of the commercial and open-source RTOS worlds. It gives embedded systems developers software that is well maintained and supported, and is easy to evaluate. Under the source-available model, developers can begin the evaluation process by downloading source code. If they decide to use uC/OS-III to develop a product, then they have to purchase a license for the software from either Micrium or an authorized distributor.
More info: Micrium Downloads