PHP NBT Decoder / Encoder
A PHP-based NBT format decoder and encoder, for the Minecraft NBT format.
A basic usage example is available in test.php. I suggest you run this script before you use the library for any other project, because this script acts as a sort of "requirements test" for your system, to ensure you have the right extensions, and that there's nothing funky with your configuration.
Requires the GMP Extension for PHP.