It was a genre that was popular in the mid-to-late '90s and early '00s
Here are some famous bands:
Korn
Static-X
Mudvayne (maybe, it's... complicated)
Slipknot
Coal Chamber
Dope
36 Crazyfists
Adema
Spineshank
Damageplan
Drowning Pool (though only on their album Sinner)
Linkin Park
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.
It's actually not. It often has rap influences, but NU Metal is basically a huge mish-mash of Hip-Hop, Grunge, various Metal subgenres, and often other stuff (such as punk).