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 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.