Since Abdullah Arif has terminated the development of PHProxy, some people made the different versions from PHProxy.
A2 is also based on the popular PHProxy script. A2 is more faster and has some more advanced features such as different combination of encryption algorithms, PHP 4 compatible and A2 doesn't need CURL installed on your server.
These advanced features are specially for Iranians to get the unlimited internet access from current situation in Iran.
Project Home Page: A2 | Get A2 at SourceForge.net