I had some blitz opponents defending the Rasa-Studier gambit lately after the moves 1.d4 d5 2.e4 c6 3.Nc3 dxe4 4.f3
The Rasa-Studier gambit often transposes to a regular Blackmar-Diemer, but there are some other lines.
a/ 4...e5 5.dxe5 Qxd1+ 6.Nxd1
b/ 4...exf3 5.Nxf3
...b1/ 5...Nf6 transposing to a Blackmar-Diemer
...b2/ 5...Bf5 and the attacker has various choices
...b3/ 5...Bg4 6.h3 seems like a Teichmann defense without Nf6
...b4/ 5...e6 6.Bd3 tranposing most likely into an Euwe defense
...b5/ 5...g6 6.Bc4 tranposing most likely into a Bogoljubow defense
...b6/ 5...Nd7 6.Bc4 making way for an Euwe or Bogoljubow
c/ 4...Nf6 5.Bc4 The O'Kelly defense
d/ 4...Bf5 5.fxe4 with white advantage
e/ 4...Nbd7 5.fxe4 with a white development lead
An interesting overview of the Rasa Stdier lines can be found here
In fact, the site hosts an important number of opening analyses, including some on the Blackmar Diemer - great information - check them all out !