Papa Sangre is a game unlike any other. Billed by the developer as "a video game with no video", it requires you to navigate through a world, blind, using only sound to guide you. It manages that with its proprietary 'Papa Engine', an audio engine that allows your regular stereo headphones to immerse you in an amazing surround sound experience. You really have to hear it to understand how impressive it is- and how scary, as you hear things moving around you in a world based on the Day of the Dead. The sequel, Papa Sangre II, is even more impressive, and stars the always-dying Sean Bean as your narrator as you land in the world of the dead and try to fight your way back alive. Today developer Somethin' Else has made it free, for the first time ever.
The game is free today only (Thursday, March 27th) so get on your phones right now and start downloading! It's usually $5 so this is quite a deal.
Navigating a game using only your ears is a pretty amazing experience. It would be surprising if more developers didn't start licensing this engine for their own games, because the quality of the surround sound with just binaural audio hasn't ever been this high.
If you enjoy it I'd also recommend you check out The Nightjar. It's a very similar experience to Papa Sangre but it's sci-fi themed, with you exploring an apparently abandonded spaceship. You'll battle with the ship's on-board computer and listen to your guide (here voiced by Benedict Cumberbatch) to help figure out what's going on.
This is one of the reason the iOS platform is so great- developers are trying out all these unique concepts. Make sure not to pass this up.