If speed isn't an issue you could try Cygwin which comes with gcc which includes a fortran compiler. I mention speed because IMO apps running under cygwin are noticably slower than 'native' ones. And ...
With the rise of WebAssembly (wasm) it’s become easier than ever to run native code in a browser. As mostly just another platform to target, it would be remiss if Fortran was not a part of this effort ...