This is modeled after the Lilypad hardware, and fits nicely on top of the plastic case of the microcontroller, allowing it to be used in a breadboard ... is a full Arduino, but the circuit board ...

[Aniss Oulhaci] demonstrates this with a simple HF SDR receiver built on a breadboard. An Arduino is used to control the SI5351 clock generator, which in turn is controlled by the same program ...