According to the post on Nintendo’s site:
The Legend of Zelda: A Link Between Worlds is GameSpotâ€™s 2013 game of the year! We want to celebrate all things Hyrulian, so for a limited time weâ€™re offering The Legend of Zelda: Four Swords Anniversary Edition for FREE!
I played a little of Four Swords back when it came out but never got a chance to play it very much. Now that we have four 3DSes in this household, we are always looking for ways to play something together. Having a little four-player Zelda should be great.