Icelandic-Palme Gambit

The idea

After 3.c4 e6 4.dxe6 Bxe6 5.Nf3, White has an extra pawn and Black has a big lead in development, with open lines for the bishops and the e-file against White's king. Wikipedia calls 5.Nf3 the critical line.

Plans for White

Develop quickly with Be2 and castle, and give back material if needed to get the king safe. The extra pawn only matters if White survives the opening, so safety comes before keeping material.

Plans for Black

Develop with ...Nc6, ...Bc5 or ...Bb4+, castle and put a rook on e8. Black's pieces are aimed at White's king, and Black wants to attack before White finishes development.

Watch out for

For White, the e-file and f2. With Black's rook on e8 and bishop on c5, a quick Qe2 or castling is essential, or Black's pieces break through.

For Black, a slow attack. If White develops and castles safely, Black is a pawn down without enough to show for it.