GBADev has an annual competition to create home brewed GameBoy games. Instead of giving out cash and flash cartridges the aim is to manufacture a batch of 500 cartridges with the top entries (a “multi-cart”) complete with cart sticker, manual and box. The cartridges will be manufactured by an “independent party” (not Nintendo). The cartridges are in, you can order them now. The games look great. Link.
Best Home Brew Gameboy Games on a Cartridge