Is this the only opening that allows one side to end up with three knights? In Queen's Gambit Declined, Albin counter-gambit, Lasker trap, black ended up with three knights, which should be rare. Here white should not capture the additional knight in the next move (8. Rxg1 Bg4+ and black is winning). Are there any other openings that one side ends up with three or more knights?

[FEN ""]
1. d4 d5 2. c4 e5 3. dxe5 d4 4. e3 Bb4 5. Bd2 dxe3 6. Bxb4 exf2 7. Ke2 fxg1=N
As @JossieCalderon pointed out, any opening could end up with three knights for one side. This would always require a knight promotion of some sort. Usually, knight promotions occur to


Give check to the opponent immediately to move the king to another square or to save a tempo.
Avoid a knight fork from the opponent, or give one of your own
Avoid stalemate
Give checkmate


I think, however, that you are also asking if there is another opening where knight promotion occurs in the opening phase of the game. The answer is  most likely "no".