As part of Nintendo's celebration of the Zelda franchise's hitting the quarter century mark this year, it is offering an updated version of The Legend of Zelda: Four Swords Anniversary Edition for free to 3DS, DSi and DSi XL owners between September 28 and February 20, 2012.
Originally the bonus material for The Legend of Zelda: A Link to the Past port on the Game Boy Advance and later a GameCube stand alone title that uses the Game Boy Advance as a controller (sound familiar?), this reincarnation of Four Swords will allow up to four players across generations of the handheld console to work together over Wi-Fi, to help Link restore peace to Hyrule. Or, you can opt for single player mode when your friends are too busy to join your quest.
Downloading the game is simple as long as you have a strong wireless Internet signal and your DSi or 3DS with you. You will find the DSiWare title in either the Nintendo DSi Shop via your DSi or DSi XL, or the Nintendo eShop on the 3DS after you tap on the Zelda icon.
Updated @ 7:00pm PT: To clarify the heritage of the game. (Thanks @JSDude1!)