Music you describe, not music you write. Pick a feeling and it works out the notes, in layers a game can bring in as things get worse.
Piece
Layers
Everything happens in this tab. There is no server, nothing is uploaded, and once the page has loaded it works with the network switched off. Export gives you one audio file per layer plus a manifest, which is what a game needs to mix them itself. Built by Dale Mooney, and there is a write-up of how it works.
Pressing a track