RIOT is a small, open-source software operating system for networked, memory-constrained systems with a focus on low-power wireless Internet of Things (IoT) devices. RIOT sometimes called the Linux of the Internet of Things.

RIOT allows application programming with the programming languages C and C++, and provides full multithreading and real-time abilities. It allows developers familiar with POSIX or Linux to begin developing for IoT devices with no learning curve. 

It is based on a microkernel architecture which comprises thread management, a priority-based scheduler, a powerful API for inter-process communication (IPC), a system timer, and mutexes and provides data structures (priority queues, hash tables,, bloom filters), a shell, network stacks, and support for various microcontrollers, radio drivers, sensors.

Learn more about RIOT and check out the GitHub repository.