Zephyr RTOS

Zephyr is an open-source real-time operating system for embedded systems and IoT devices. Unlike a bare-metal approach (where you manage all timing and interrupts), Zephyr provides abstractions for multithreading, synchronization, memory management, and hardware interaction. It's lightweight (50–500 KB depending on features), supports 300+ hardware boards (Nordic nRF, STM32, NXP, Espressif, etc.), and includes built-in networking stacks (Bluetooth, WiFi, Thread, ZigBee), security primitives, and device driver frameworks. Zephyr is sponsored by the Linux Foundation and is increasingly used in production IoT, wearables, and real-time systems. It bridges the gap between minimal FreeRTOS and heavyweight Linux for devices where you need both real-time guarantees and moderate complexity.