1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6 4. 0-0 Nxe4 5. Re1 d5
6. Bxd5 Qxd5 7. Nc3
This is a system against the Two Knights Defense. Paul Morphy popularized this line. You also need to know the Max Lange Attack in case your opponent plays 5. exd4.