Previewed earlier this year, Moshing Cat Studio’s Squarewave Maker is designed to put a new spin on the rhythm game concept.
In the first instance, you can just play through the supplied side-scrolling levels, with the music sounding better the better you perform. However, you also get a set of design tools so that you can create your own music and levels. Then you can become part of the Squarewave Maker community, sharing your levels, songs and synthesizer presets and downloading content from others.
The music creation tools in the software seem pretty comprehensive - you get a piano roll, mixer, synths and effects - and you also have plenty of control over the look and feel of your levels.
You can find out more and back the project on the Squarewave Maker Kickstarter page, where a CA$25 pledge will hopefully get you the game in October 2019. It'll run on Windows.