Out of the box, the Analogue Pocket can play all the original run of Gameboy and Gameboy Color games, and has an audio sequencer as well.
With some adapters, you can also play other handheld titles from the Game Gear, Neo Geo Pocket, and Atari Lynx.
Taking a note from the PSP and the Nintendo Switch, you'll also be able to buy a separate dock that connects to your TV and USB/Bluetooth controllers for playing your portable games in a non-portable fashion, if that's your thing.
This isn't a portable emulator-- Analogue have engineered their own chips to play these games. And ... just look at it. That's a beautiful piece of hardware.
I'm going to spend the time between now and when this releases trying to tell myself that I don't need it.