Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. d4
Scotch Game 
This aggressive move practically forces Black to play 3...exd4 which releases central tension very early. This should lead to a very open game with a lot of space for both players.
A few tries have been made with 3...d6 but this move is considered inferior because of 4.dxe5 dxe5 5.Qxd8+ Kxd8 6.Bc4.
3...Nxd4 is a playable good move. 4.Nxd4 exd4 5.Qxd4 and some good players believe that black nearly equalizes in this line.
Also seen after 3...Nxd4 is 4. Nxe5, after which black will have to move the knight.
Theory table 
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- Nunn's Chess Openings. 1999. John Nunn (Editor), Graham Burgess, John Emms, Joe Gallagher. ISBN 1-8574-4221-0.
- Batsford Chess Openings 2 (1989, 1994). Garry Kasparov, Raymond Keene. ISBN 0-8050-3409-9.