There's several! We tried all of them without much luck :(. The most complete seems to be the old flang, which was basically an open sourced version of the PGI compiler hacked up to generate LLVM IR by concating strings to generate textual LLVM IR. However, that project is basically abandoned and also depends on LLVM 7, while you probably want at least LLVM 10 to generate good code for Apple Silicon, so somebody would have to do that porting work, which doesn't seem like a worthwhile investment.
Hopefully apple will do something about it as they did advertise their new system would be great for machine learning and all, which seem to be moot without many popular numeric libraries that directly or indirectly use fortran. Would be great if clang/llvm suddenly gain a great open source fortran compiler just because apple moves to arm.
