Rare 1. d4 Gambits

After 1. d4 Nf6 2. f3 d5 3. e4 dxe4 4. c4, Black can lead the game to completely new variations, which are often similar to the Blackmar-Diemer Gambit, except that White has here played c4. By playing the queen's bishop to f5 or g4, Black can avoid French-like lines. Of course, the lines are not pure DDG, but because of the similar ideas, they are useful subjects of investigation to DDGers. 1. d4 Nf6 2. f3 (Paleface Attack) d5 3. g4 (Gedult Attack) might also transpose to this line if White played e4 later. Here are also glanced at 1... d5 variations.
B

4... exf3

4... exf3 5. Nxf3

4... Bf5

4... Bf5 is similar to the Vienna Defence. 1. d4 d5

1... d5

After 1. d4 d5 2. e4 dxe4, Rebel Decade (ELO about 2200) actually suggests 3. c4, so it cannot be that bad. Moreover, as Black it plays 3... e6, transposing nicely to the DDG. Other replies are also interesting:

3... e5 4. d5