Anyone tried this ? It's an app on DSi and 3DS that let you program your own stuffs in BASIC !!! I know there is a MML editor somewhere too !!!
http://www.petitcomputer.com/
The cool thing in this is that you can copy programs with QR codes instead of programming everything by hand !
If you want some synths you can check these pages :
http://www.geocities.jp/sp1_ssr/px7.htm
http://home.nshdot.com/auduino-petit-3
http://d.hatena.ne.jp/eidaht/20120630/1341016869