Ten years ago, "emulating a Game Boy on your watch" would have been a punchline. Today it is a small but real category. A handful of developers have squeezed genuine Game Boy, Game Boy Color, and Game Boy Advance emulation onto a screen the size of a postage stamp, and some of it actually works.
Here are the emulators worth knowing, split by platform, plus our pick for each.
First, the honest part
Emulators are legal. The games are the catch: only load ROMs of titles you actually own, ideally dumped from your own cartridges. Every app below expects you to bring your own files, and none of them hand you copyrighted games.
Set your expectations too. You are playing on a one to two inch screen, with touch controls, on a battery that was never built for a three hour session of Pokemon. These are a delightful party trick and a real way to squeeze in a few minutes of a classic, not a replacement for a handheld.
Apple Watch: ArcEmu
On Apple Watch there is really one name, and happily it is a good one. by bills itself as the first emulator for Apple Watch, and it covers Game Boy, Game Boy Color, and Game Boy Advance through the well respected mGBA core.