http://zelda.nintendo.com/top.html
As part of the celebration, a slightly enhanced version of the GBA Four Swords (the one that came on the GBA Link to the Past cartridge) is available for free for DSi and 3DS. It supports wireless multiplayer, has singleplayer support, and adds some maps themed after areas in past Zelda games.
http://zelda.nintendo.com/fourswords/