YARG - Yet Another Rhythm Game. Like Guitar Hero/Rock Band (way better than Clone Hero) - open source. Guitar, Bass, Drums, Keys, Vocals.

I think it’s still being worked on, but some Devs have been hired for the next big rhythm game - if I understood correctly - so the development has slowed some.

You can get quite a lot of songs for free with it, there are some real bangers and it’s tons of fun (or go sail the high seas and get what feels like infinite songs, including those from the popular plastic instrument games). Also runs really well on my potato laptop…