What is the current state of the DS "modding" scene?
My sister has a Nintendo DSi that she wants to be able to download games for and play them on. This was pretty easy a few years back when we had a household full of DS Lites; as far as I can remember, all that was needed to copy some ROMs over were R4 cards, but doing some cursory research, it looks like the DS modding scene now involves something called flash carts that I've never heard of before, and the scene generally seems to have gotten a little more complicated.
With that in mind, I'd really appreciate it if someone could give me a rundown on where the current DS modding scene is atm, and what's going on with it. What exactly are flash carts, and how do the older cards like the R4 now fit into the equation, if at all? Is it still possible to use R4-like cards without the use of a flash cart, and if so, which is currently the best on the market?
Would really appreciate being brought up to speed. Thanks!