That’s actually got to be a record. I only received my DS yesterday and I’ve already ordered a R4 DS card.
To backtrack a little, R4 DS allows homebrew to be run on the DS console. Similarily, how homebrew can be run on a PSP, only no equivalent is required to be purchased. For the PSP, the process of downgrading and upgrading is a lot more complicated but at least it’s free (Unless you opt to buy a Pandora battery). Whereas the DS doesn’t have a conventional memory card slot, so in order to get anything onto it, an adapter is needed.
This is where the R4 DS (or Revolution for DS) steps in. It’s basically a MicroSD card adapter for the DS console. Put whatever you want the DS to run on the card and then fit it into the R4 card and in turn, insert that into the DS. When you turn the console on, It should boot from the memory card and allow you to play homebrew games and applications. And commercial ROMS… but not unless we have purchased a legitimate copy of the game in the first place, remember.