The twentieth-anniversary edition of 6 nimmt! includes ten joker cards numbered 0.0 to 0.9. Each player starts with one in hand, and the others are shuffled into the deck. Each player then receives ten cards as normal.
During play, any joker card played is lower than regular cards, so it's placed first and whoever played it can place the card at the end of any desired row.
All other rules remain the same.