Ran across this the other day, and it really is wonderful.  It is a
virtual 40h for the Nintendo DS, that uses DS MidiWifi to communicate
with software applications.

Here's the link:

http://forum.gbadev.org/viewtopic.php?t=13911&sid=dff8627fd28b27afd5897c540eb48f60

Here's a Youtube video illustrating it:

http://youtube.com/watch?v=fFgQTySpY9M

I've got the app working on my NintendoDS, but haven't tried it through
my MIDI setup.  I really is nicely well done.

So, not quite a Monome app, but in the realm of things at least...

props to the author, GrizzlyAdams