equipment recommendation - Is there something that is the opposite of a teleconverter?

I shoot a Nikon D80 that has a 1.5 crop factor. I'd like to find something like a .67x teleconverter so any full format lens I attach would then have their original focal length and would in theory be faster. Does such a thing exist? If not, is it a matter of physics or patents/marketing/business/etc?

Edit: Thank all of you for the information so far! If I'm understanding things correctly it isn't possible to make a simple focal reducer for DSLRs, but is it possible to make one with some complicated optics? Do focal reducers exist for Nikon F mount cameras, even if they don't aid or slightly reduce image quality?

Would it be possible to have a DSLR camera body specifically designed to have the properties of having a built in focal reducer? Eg a camera body with a reduced size sensor, but having it moved, and the body would require full frame lenses.