I've just spent far too long writing the beginnings of a ridiculous music game for web browsers. You use either a MIDI keyboard or the computer keyboard (a s d f g h j k). The game plays a bar of random notes and you have to play it back, correct notes and correct timing. As you level up, the patterns get more rhythmically complicated. If you make 5 mistakes, game over; you have to start again. Still probably a lot more to do to make this more interesting, but I'm curious as to whether anyone finds this remotely worthwhile.
One challenge right now is how to calibrate if you don't have absolute pitch. I feel like I might need to add some sort of screen where it plays you a few notes until you find the right ones or something. For now, note that it's in A minor, A3 to A4.
https://files.jantrid.net/simus/
Simus

@jcsteh That's cute. I noticed I lost a round and a note kept playing for some reason, had to Ctrl+F5 to stop it. Are there levels that you have to play more than one note at a time?
@Jage Yeah, will try to fix that bug. Not currently polyphonic levels, but that's an interestingly nasty idea.
@jcsteh I'm here for interestingly nasty ideas. You could always implement a cord CAPTCHA.
https://bestmidi.com/captcha/cords.htm
Chord CAPTCHA

@jcsteh Seriously, it's a cool idea though and the music gives it some life. Can you control the diffficulty, i.e. make level 1 on expert start faster
@Jage I'd need to make more loops for different tempos, but yeah, I'd like to do that when I get time.
@jcsteh Ah didn't know if you wanted to just apply some tempo compression, but that probably makes the loops sound off.
@Jage Yeah, I tried that with granular synthesis and the timing felt a bit wrong. I guess I could render the same loop from REAPER at various tempos.
@jcsteh Ya even if it's just 2, that being said, I guess I should beat the game as it is before asking for expert mode lol.