PokeDaisy

PokeDaisy is a Game Boy, Game Boy Color, GBA and Nintendo DS player for Android handhelds with two screens or one, made for Pokemon FireRed, LeafGreen, Emerald, Ruby, Sapphire, Red, Blue, Yellow, Gold, Silver, Crystal, Platinum, HeartGold, SoulSilver and popular ROM hacks of every generation. Next to the game runs a live companion that reads it as you play: your party, your bag, the map, battle matchups, your Pokedex, and a spoiler-free guide. Everything is drawn in the game's own menu style.

Two screens (AYN Thor, Retroid Pocket Duo, ...): the game on the top screen, the companion gets the bottom one to itself.
One screen (Retroid Pocket 6, phones, ...): the companion opens as a window over the game or a panel beside it (under it on a phone held upright), and a HUD keeps your party, a minimap and your bag on the game screen. The quick menu, one button away, opens your PC, flies, rides your bike or fishes, and battle buttons fight, switch or run right beside the battle.
A phone and a TV: cast or plug in a TV and the game goes on the big screen, the companion stays in your hand.
DS games (Platinum, HeartGold, SoulSilver): on a two-screen handheld the DS's touch screen goes on the bottom screen, and one tap there swaps it for the companion and back. The companion also opens over the game, like on one screen.