According to its creators, the currently-crowdfunding PocketSprite is the world's smallest playable emulation device. It isn't just tiny, though – it plays all Game Boy, Game Boy Color, Sega Master System, and Game Gear games, plus users can upload other games via Wi-Fi.
Originally developed as a proof-of-concept by engineer/hacker Jeroen Domburg, the PocketSprite features a full-color OLED screen, an 8-bit speaker, a dual-core 240-MHz ESP32 processor, and 520KB of RAM. It comes preloaded with the GNUBoy and SMS Plus emulators, while other game ROMs can be added over-the-air using Windows, Linux, Mac, or Android systems – users connect to the PocketSprite's Wi-Fi network, upload the ROM through PocketSprite's web interface, and start playing.
Once they are playing, it's possible to halt the game and turn the device off when need be, then later turn it back on and pick up where they left off.
Because all of the hardware and software are open-source, users are free to pull the thing apart and mess around with it to their heart's content. There aren't any exact figures provided on battery life, other than that one charge of the integrated lithium-ion battery should provide "hours of gameplay and months of standby."
If you're interested in getting one, a pledge of US$55 is required. Assuming all goes according to plan, it should ship in May.
You can see the PocketSprite in action, in the following video.
Sources: PocketSprite, Crowd Supply
