KISS is very similar to Niagara, and is FOSS. I have used it for years

https://kisslauncher.com/

https://github.com/Neamar/KISS

The game is there, but the link is redirecting to the main page for me right now

https://www.humblebundle.com/store/hollow-knight-silksong

EDIT: Archive from earlier today when the “ADD TO CART” button was working https://web.archive.org/web/20250904142914/https://www.humblebundle.com/store/hollow-knight-silksong

I played many hours of the original, and do not expect to ever try this new one. Even if I got it free with a bundle or something… I just didn’t enjoy playing the original enough.