PokeMMO is a game created by fans, letting you play games from the 3DS Pokémon saga on your Android smartphone, where you can interact with other trainers by chatting, fighting, and exchanging the Pokémon you find.
This game has an important requirement, however: you need to have the ROMs for the games in question available on your smartphone. For the game to work, you absolutely must have the ROM for Pokémon Black/White, and you can get additional content for the same game if you also have FireRed/Emerald, plus better graphics with HeartGold/Soulsilver.