Think RPGMaker, only.. for the Nintendo DS! Virtual Game Maker DS allows you to create your very own homebrew games for your DS. This should be installed on your PC. There's been quite a hefty amount of changes for v0.95. One of the more recent changes is DLDI support.

Coming soon (TODO LIST):
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-Full objects system (you can find, buy, sell or let them...)
Change chipset
In-game interface (pause menu)
Objects & equipment effects in-game
Sell, and Buy instructions for equipment.objects
Full debug (just to remove the pink bug)
RPG battle system

You can view tutorials via the Globoeil's dev website here: http://www.globoeil.fr/vgmds/Tutorials.htm