RISC-V is an open-source instruction set architecture (ISA) based on reduced instruction set computing (RISC) principles. It's gaining popularity in the microcontroller (MCU) and embedded systems world due to its open nature, which allows for customization and avoids vendor lock-in.

There are several RISC-V based MCUs available in the market, such as the CH32V003DS0, SiFive E31 and E51 cores, which are commonly used in development boards and IoT devices. These MCUs offer a good balance between performance, power consumption, and flexibility, making them suitable for a wide range of applications.