Thanks :) I'm working on a homebrew Gameboy game but I'm not quite ready to make the music for it yet.
According to this thread Deflemask can be used to make music and put it in a game, so I'll keep it in mind!
https://www.deflemask.com/forum/general/can-music-made-in-deflemask-be-added-to-a-homebrew-game/
TL;DR
Deflemask is a multi-system tracker available for Windows, Mac, Linux, Android and IOS. There are two versions: the new paid one with a lot of features and the legacy which is an older unsupported but still works great application.
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DefleMask is very good, but before you buy the new version (it's £10, or whatever the equivalent is for your currency), i recommend playing with the legacy version which is free. I personally still use the legacy version. With DefleMask you can make music for a lot of systems in one app (right now you can make music for the Sega Genesis + Without Channel 3, Sega Arcade, Sega Master System, NES, Gameboy, Commodore 64, NEC PC-Engine and on the new version you can make music for the NEO GEO Pocket).
The first hyperlink in the comment should tell you everything. The new version has a ton of new features which are really cool (Check one of the videos on their homepage), but if you're like me and don't feel like paying then the legacy version will do just fine.