Sorry if this shouldn't go here, I just thought it might be well received given the audience 
I powered up my 3DS for the first time in about 6 months 
and I found Petit Computer. I haven't gotten into it too much but it seems to be a well documented legit (not homebrew) BASIC interpreter for the 3DS/DSi.
idk I think it looks pretty cool. You can share programs via QR codes too.
Link: http://www.petitcomputer.com/