R4DS - the Revolution has begun for your DS/DS Lite

Wow. This thing is so cool!

The R4DS turns your Nintendo DS/DS Lite into a portable media player, and so much more.

R4DS.net puts it this way.

The R4DS Cartridge is the current top-of-the-line in DS SLOT-1 flash carts. It is just an amazing little device like original DS cart size, it is a complete solution with no need to purchase any additional components or deal with any messy software and truly the easiest media enhancer you have ever done; To simply put it, this is a must have peripheral for any regular DS/DS lite owner.

I've got one. It's cool. You need one. Now.