A demo of the Korg DS-10 Synth using four units.
XSEEDgames has several more Korg DS-10 demos at YouTube.

cellsDS is a free programmable grid-based music sequencer for the Nintendo DS.
Description:
cellsDS is six sequencers in one, with each sequencer being controlled by a user definable Lua script. It is the peculiar anti-social stepchild of the Tenori-On and Monome.
Features include:

Dead simple user interface.
Ability to create your own unique sequencer rules using the Lua programming language. [...]

William H of InsideSynthesis does a great video review of the new Korg DS-10 synthesizer/sequencer for the Nintendo DS.

The Korg DS-10 Synthesizer - a software synthesizer for the Nintendo DS - is available now for order and will be shipping at the end of September.
Features:

Professional-grade music tool software for the Nintendo DS
Two patchable dual-oscillator analog synth simulator, -part drum machine that uses sounds created with the analog synth simulator
Six-track (analog synth x [...]

DS Lite Orchestra - Cicadas - performed on the Korg DS-10.

“Do you think this is just yet another toy synth?” asks Denkitribe. “I don’t think so. This is a very serious virtual analog synth.”
Looks pretty cool from the demo.

Remain Calm has put together a list of its top 24 music apps for the Nintendo DS:

bliptracker - a drum machine & sequencer
dsmcu - MCU-compatible mix controller
Protein[DS] - sample looper, scratcher, glitcher
nitrotracker
kaosDS - converts touchscreen data into midi over wifi
sampling keyboard
dstep v2 - a visual sequencer
glitchDS - a cellular automation sequencer
repeaterDS - stuttering sample player
midipad [...]

This episode of the 1Up show - an online video game show - features a look at the new Korg DS-10 synthesizer, which runs on the Nintendo DS platform.