.nds is the rom itself (for use with non-retail cards like R4, Acekard, etc) and .sav should be the save files. This tool works with all DS games that I've tested (including those that use the newer IR cart like HGSS/BW, which this was specifically made for). This tool does not export .nds (rom) files to my knowledge, it is only for saves. The .sav should be compatible with Acekard for sure, and I believe most cards use similar files. I only speak for the Acekard 2i because it's the only one I own myself.