Grainstorm

Use as/for:
• Tool for Sound Design
• Experimental Musical Instrument
• Fun

Key Features:
• Fast and lightweight
• Four tracks
• Stereo Mode
• Loads sound files of up to seven minutes length in any audio format
• Effects like Convolution Reverb, Channel Vocoder, Phase Vocoder

First use instructions:
1. Press POWER. Upper right power button turns on audio engine which is TURNED OFF on startup to save battery.
2. Press EJECT. Load a sound file.
3. Press PLAY.

A manual can be found here: https://grainstorm.rocks.me/instructions.html

There is an In-App-Purchase which among other things lets you record the output. Please consider the free version as a demo version.