Newer Super Mario Bros. DS is a fan-made project that basically gives you a whole new Mario game for the DS (only you actually play it on PC or Mac).
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Newer DS is not technically a standalone game; instead, it’s a patch for the original ROM that was made using the New Super Mario Bros. Editor. There are 80 levels across eight world maps, some changes to graphics and even a new soundtrack.
It’s made by the same team behind Newer Super Mario Bros. Wii, which came out a few years back.
Here’s a trailer showing the game in action, and you can grab it here.