entry point (_main) undefined xcode 6

I can't for the life of me find a solution to this! I'm using Swift. All of a sudden I get this error:

Undefined symbols for architecture i386:
  "_main", referenced from:
     implicit entry/start for main executable
ld: symbol(s) not found for architecture i386

It doesn't matter what simulator/device I try to run for, I still get it:

Undefined symbols for architecture x86_64:
  "_main", referenced from:
     implicit entry/start for main executable
ld: symbol(s) not found for architecture x86_64

What is this?! I've almost removed everything from my project. I.e. all frameworks and everything. It's still there.

Please help me