1.The DSLink is a 1st generation storage device used to run Nintendo DS homebrew. It allows the running Nintendo DS games and programs created by unofficial developers. It also allows the running of Nintendo DS game ROMs.
It's an old DS flashcart. Here's an official GBATemp review.
If you have one, then you could use it, I guess. It's probably missing a lot of features that the newer flashcarts have, though.
There's also an application that downloads small homebrew files over the network. It's used for exploits where you don't have much space for a payload.
It is a firmware that you can install on your WIFIcard that sends over small DSImode homebrew to ram so Dsi gamecard exploits(the biggest loser, etc.) can run a bit more homebrew than fit on their save file.