Open64 is described as 'open source, optimizing compiler for the Itanium and x86-64 microprocessor architectures. It supports Fortran 77/95 and C/C++, as well as the shared memory programming model OpenMP' and is an app in the Development category. There are four alternatives to Open64 for a variety of platforms, including Linux, Mac, Windows, BSD and Cygwin. The best alternative is GNU Compiler Collection, which is both free and Open Source. Other great apps like Open64 are clang (Free, Open Source), LLVM (Free, Open Source) and Portable C Compiler (Free, Open Source).