Kudos to you for asking this interesting question. There's also the expression "To give props," which basically means to same. It's meant to compliment someone for doing something. "Kudos to you for finishing work today when you felt all sick." Basically, "I really got to give you credit."

To add on to the first answer, it also serves the function of an informal "Congratulations!" So where in a formal setting, you would say something like "Congratulations on getting that promotion," in a casual/friendly setting, you could say "Kudos on getting that promotion!"