FreeRTOSTM includes official ports to 26 architectures and receives more than 77,500 downloads a year. It is a popular, portable, open source, royalty free, mini Real Time Kernel - a free to download and free to deploy RTOS that can be used in commercial applications without any requirement to expose your proprietary source code.
Platform: unknown; License: Modified GPL (Open Source) Licensing
Reference: https://www.freertos.org/