It is a hacked game available as a ROM for the Visual Boy Advance. Apparently people have also made it into an actual GBA cartridge: http://www.ioffer.com/img/item/955/646/31/3M8B2djwvs0XZ2d.jpg
(Note: since it is hacked an unofficial it is illegal for them to sell/distribute it so I would strongly advise against trying to buy it.)
A fan created Pokemon game, online.
