As it turns out there are at least 2 TU devs who are kinda decent at Stepmania (and also Flash Flash Revolution was on GMT) so I am required by law to spread some knowledge about this amazing game, Stepmania.
What is Stepmania?Ever played Dance Dance Revolution, the game where you step on arrows to the beat? Yeah, it's basically that but for PC and you can play it with your keyboard and stuff. Also it has extensive custom song and modding support, and because of that combined with the fact that you can play it with a keyboard, its charts have gotten ridiculous.
(Content warning: some swearing and some kinda loud audio. This is a meme chart, but I’m sure it gets the point across.)
Stepmania can be downloaded here, and Etterna, a popular fork intended for serious keyboard players, can be downloaded here. The Etterna website also has a massive repository of charts to download, covering almost all skill levels.