Not just the GBA, apparently! 3rd party handhelds like the Pocket and emulators are supported too.

From the website to the software, this looks stunning.

Tried chip music with nanoloop several years ago. Wasn't 100% for me: 1) pure chip music is too jarring for my ears; 2) it's in the name ('nanoloop'), but it pushes you toward short repeating loops. Once you've heard the same 4-bar loop a couple of hundred times, it's hard to imagine the next phrase. Feels like getting stuck. This has a 128 pattern * 16-step sequencer. If those patterns are easy to chain, then this could be really nice for longer phrases.

Can anyone comment on how much effort goes into flashing a cartridge? I've never done it. Back in the day, I just ordered nanoloop straight from the website.