The Legend of Zelda: Four Swords Anniversary Edition is free on the 3DS eShop this weekend. Nintendo tweeted as much today, saying the offer is good through February 2.
The game is a re-issue of the multiplayer version of Four Swords that was packed in with the GameBoy Advance port of The Legend of Zelda: A Link to the Past. Unlike the original multiplayer-only game, 3DS owners have a single player component in which they can collect rupees and slash at enemies.
Four Swords arrived on the eShop for DSi and 3DS owners in September 2011, and was made available for free until late February 2012. So yes, Nintendo is giving away a game that they've given away before, but we're not ones to complain about free things.