EFA Linker was one of the best carts available back in the NOR flash days (all internal storage, no removable SD or other cards). There was a 256 mbit version and a 512 mbit version. I had both at one time, but my 512 went tits-up. The 256 mbit is still in use (by my daughter - I use an EZ Flash IV). Although the space is limited, because all the games are loaded on the internal memory there is no wait for loading. If you install one 256 mbit game, such as Mother 3 or Riviera, there is no loader and the game boots when the console is started, just like a retail cart. (This can also be done with smaller games, as the client software allows you to choose whether to implement the loader. With 256 mbit games, there's no option as the one game fills the cart.) With anything smaller than 256 mbit, the number of games you can have installed obviously depends on the size of the games. Anything from 2 - 8 games is possible. The EFA Linker is also capable of playing DS games from slot 2 if the DS has a PASSME cart (I think that's the correct term, it's been a while) in Slot 1, though the company went out of business sometime during the DS lifespan so I would expect support is limited to games that were released before the company closed.
There was an EFA Linker II that came out in the early days of the DS, but it never sold well and as I said the company closed down. It had a 1 gbit internal memory.
Another top-drawer line of carts back in the NOR flash days was the EZ Flash Advance. There were three generations, and AFAIK these were the predecessors to the EZ Flash IV. Like I said above, I have an EZ Flash IV and I agree with the others recommending it - there's no reason to bother with trying to find any of the old school GBA carts.
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