Krypteria...

"Mainstream" is so relative as a term, though. There are people I know who consider Nightwish to be mainstream, despite them never having had anything in the UK chart to my knowledge and so don't fit any meaningful definition of "mainstream".

I think once we understand how "mainstream" and "alternative" music works, we'll understand everything about the human condition. I could re-write all of skepticism and human rationality with this as the analogy.