phpShield is described as 'PHP Encoder from phpSHIELD, converts PHP source code into unreadable bytecode, providing php script protection and compiling at a great price point'. There are four alternatives to phpShield for Linux, Mac, Windows and Online / Web-based. The best alternative is phpBolt.com, which is free. Other great apps like phpShield are Turck MMCache (Free, Open Source), Sourceguardian (Paid) and Transfon Swoole Compiler (Paid).
SourceGuardian for PHP allows you to quickly and securely encode, compile and encrypt your PHP files to protect not only your intellectual property, but also sensitive information such as database passwords.
Transfon Swoole Compiler (TSC) is a PHP source code encryption, code-protection and licensing solutions, including PHP code compiler and PHP code loader. It is designed for plugins or extension developers to protect source code and manage licenses.