You don't need any software to decode. PHP has a limited number of built in functions like base64_encode() , which is normally used to embed images in css. Ofcourse there is base64_decode() as well along with plenty of website that let you do this online.
The code in the beginning of this thread is a simple cypher A= J, B=2 ... something along that line. you can even get some of it since a piece of the code looks in the same format as http://www + .com .. that's 7 letters, 25% of the alphabet decoded
The variable holding the code is $__X__ .. so download notepad++ , and scan for $__X__ and go to every instance and see what's going on. Your goal is to find where the decoding takes place , there will be comparison and sorting of arrays, and thats when you add a line to the code to var_dump($array_name_to_print); or for variables print_r($variable_you_want_printed); Add both of those behind every variable/array that interacts with $__X__ and eventually you will see the decoded version. It's not rocket science. Since the browser will not read code, at some point it has to be decoded and sent to your browser, use wire shark to capture every tcp/ip request... bit more complex. easier to just hack at it with the two commands.