F80 is Microsoft Fortran 80, in case you don't feel like clicking to make sure. And it is a disassembled binary, not the original source code, in case you were hoping.
It would have made very little sense for a company willing to make a FORTRAN 77 compiler to target already obsolete microprocessors, instead of targetting the state-of-the-art Intel 8086/8088 or Motorola MC68000.
The Microsoft F80 compiler would have indeed been useless for anyone having unlimited access to a CPU more powerful than a Z80.
Nevertheless there were many who had to be content with an 8080/8085/Z80. For them, there was nothing better than Microsoft F80 for serious numeric computation.
FORTRAN IV was the language in which a huge amount of high quality numeric computation libraries were easily available. No library was available in Fortran 77 at that time.
The language implemented by F80 was pretty standard. It lacked many extensions frequently provided by other compilers, but that did not matter much, because the libraries that you would want to use were written to use only strictly standard features, and not vendor extensions.
Before using MS F80, I had used IBM mainframes and DEC PDP-11 minicomputers. I do not remember any special difficulty in porting the IBM/DEC Fortran programs to MS F80.
Obviously, an 8080/Z80, when doing floating-point computations, was between 10 times and 1000 times slower than an IBM or DEC computer with hardware FPU.
Even so, for me, passing to MS F80, where I had exclusive access to the computer 24/7, was a huge progress in comparison to using a shared mainframe or minicomputer, and I could be much more productive, despite the slow computer.
I'm glad that you were able to port your code from DEC FORTRAN IV. I may be younger than you because I learned FORTRAN 77 first, but IIRC Microsoft's F80 had some serious shortcomings and was not a "full" implementation of FORTRAN IV. That's probably why they called it "FORTRAN 80" instead.
- No COMPLEX type - Specification statements must be ordered FUNCTION/type/COMMON/EQUIVALENCE/DATA/statement functions - differing storage requirement for types
then again, even MATLAB (for example) doesn't need COMPLEX