Yes, it is an Arduino board, but I omitted to mention in the title not to discourage those who doesn’t have one, because the project needs just a few passive components beside the ATmega168 you can even build it on a breadboard.
The project is a great example of the AVR micro controllers speed since it does a real-time audio signal sampling and output on the PWM channel, it has also a couple of audio effects like reverberation, overtone. Because it isn’t a dedicated audio DPS it has some limitations, like 15kHz sampling rate, 512byte ring buffer, 8bit PWM which handles the digital to analog conversion, so don’t expect for high quality sound output. Consider this a scaled down audio effect generator, it covers the basic effects and is a great introduction for more complex audio processing
ATmega audio processing: [Link]