Variations:

Open: In this variation of the game, instead of having to make 30 points for your initial meld, you need to make 50 points. Also, you are allowed to take the tiles your opponent doesn't want anymore. 

Foot: To play a foot you cannot make sets or groups, you have to create them without your opponents or opponent knowing what you are doing, and in the end when you think you have one you need to declare "Rummikub" and you and your opponent need to reveal your tiles. 

Hands: For this game your play is closed, meaning just like when playing Foot you don't expose your tiles until you declare "Rummikub". Furthermore, you shouldn't use too many jokers, because they will take away the value of the play.