The links download zip files, which should open on Mac, PC and Unix/Linux machines. SNAP is a Perl program, so to run it you need to have Perl installed on your system. It is usually installed on Linux/Unix, but for PC or Mac use you may have to download it. Perl is available for free at www.perl.org. Vespa is a compiled C program, the zipfile contains separate versions for Mac, PC and Linux/Unix. If you run the correct version and still have trouble, let us know!