Wiisp Synth is a free Android app developed by thIIIrd that provides a simple and minimalistic synthesizer experience. The app is built with Pure Data and is controlled by sliders, which allows for a reactive and intuitive user experience.

The design of Wiisp Synth features two oscillators that are sine waves with adjustable pitch. The second oscillator has a higher pitch range, providing a wider range of sound. Both oscillators are directed to a delay, with optional FM from oscillator A. The frequency of a resonant lowpass filter is controlled by the LPF slider and is bypassed when the slider is set to 0. The filter has FM input from each of the oscillators, providing even more sound customization. Glide creates a smooth transition between changing any of the values, making it easy to create unique sounds.

Overall, Wiisp Synth is an excellent option for those looking for a simple yet powerful drone synthesizer. Its minimalistic design and intuitive controls make it easy to use, while still providing a wide range of sound customization options.