UPDATE: THIS IS LIVE NOW ! (28 SEPT) Enjoy!
I've just downloaded it from the Nintendo Dsi shop on my Dsi.
It has a single player and multiplayer option.
In the single-player mode, you control two Links. Switch which Link is active by pressing the L and R Buttons, or call the other Link to your side by pressing the X Button, to safely move around together solving puzzles and avoiding traps.
To enjoy the game with 2 - 4 players, each player needs their own Nintendo 3DS, Nintendo DSi XL or Nintendo DSi system with the software downloaded to the system memory.
3DS and DSi gamers will be offered Game Boy Advance adventure Zelda: Four Swords for free in September, Nintendo has announced.
The multiplayer-focused game is being re-released without charge as part of this year's ongoing 25th Zelda Anniversary celebrations.
Nintendo are re-packaging it as DSiWare, meaning it'll be available to DSi gamers as well as to 3DS owners through the handheld's eShop.
Four Swords was initially released as a multiplayer add-on to the GBA re-make of A Link to the Past. This concept was later beefed out into a full game - The Legend of Zelda: Four Swords Adventure - for GameCube.