Project OutFox is a free BUT CLOSED SOURCE, cross-platform rhythm game. It is a fork of the OPEN SOURCE game, StepMania. It supports common key-based rhythm game formats (including 4-panel and 5-panel dance games among others), as well as keyboard and dance pad controllers.
It is customizable with user-made add-ons such as themes, and provides an integrated editor for creating your own simfiles.

Project OutFox only comes with a couple of songs, so you are expected to add your own content! There are multiple websites out there for hosting songpacks, here is one of them: https://search.stepmaniaonline.net/
There are also official Project OutFox packs here: https://projectoutfox.com/outfox-serenity

To run: Menu -> Games -> Project OutFox
To run in a terminal: ~/ProjectOutFox/*/OutFox

How to customize Project OutFox (adding songpacks, theming, etc):
https://outfox.wiki/user-guide/config/folders/

Your User Data folder is where you place custom content (like songpacks):
~/.project-outfox