Pattern based sequencer for the Nintendo DS. Free, but development has stopped as of 2010 (though info for this comes from the Dec 24 2008 update) So you're more than likely on your own.

Features (this is a quote)
- Easy to use step sequencer with up to 4 Groove Sliders per step
- 16 monophonic tracks with up to 2 sounds per track with ADSR envelopes and LFOs
- 16 variable length patterns up to 64 steps long
- 16 channel mixer with volume, mute and solo control
- Song arranger can chain up to 255 patterns each with individual settings
- WAV file support with preview in file browser with up two 2MB of sample RAM
- XY PAD real time performance interface

GrooveStep