It was a genre that was popular in the mid-to-late '90s and early '00s
Here are some famous bands:
Mudvayne (maybe, it's... complicated)
Drowning Pool (though only on their album Sinner)
many, many others
I have just gotten into it, but basically, from what I understand, nu metal is rock music with rapping. Hollywood Undead is the band that I am in love with right now. Lots of their songs are nu metal. Alternative rock is amazing too, though.