Work-in-progress
I wanted to make a game that could be played on a phone while trying to go to sleep at night. Without requiring a horrid shining light blasting me in the peepers.
It would be audio-only, controlled by a single touch area, and ignores the orientation of the touchpad.
It would be an engine for navigating a world full of objects that make sound, objects that must be avoided, objects that move, and objects that get in the way, but also objects that talk back to you.
I looked for a free game engine on Android, supporting binaural audio, and couldn't find one.
It also made me consider how many games are accessible enough that a blind person could play it. I can only think of one.
Using Google's VR stuff for 3D positional audio, with my own touch/navigation interface and engine, it's mostly working. Plenty of things would need extending/fixing to make it production-ready.