Many years ago, I had some fun training simple machine learning models on piano roll midis I'd downloaded from various public repositories.

Here's a "waltz" produced by a grid-lstm, a long obsolete LSTM variant:

https://m.soundcloud.com/vintermann/lstm-waltz

Probably more interesting to get a feel for the failure modes of old LSTM variants than for the music, but maybe someone on hacker news will appreciate it.