Go! is a PHP 5.4 library that allows developers to add support for aspect-oriented programming (AOP) to their PHP applications. It doesn't require PECL extensions, Runkit, evals, or DI containers. The code with weaved aspects is fully readable and native, and can be easily debugged with XDebug. You can debug either classes or aspects. It can potentially be installed in every PHP application because you don't have to change the application source code at all. As an example, with the help of 10-20 lines of code it is possible to intercept all of the public, protected, and static methods in all classes of an application, and display the name and the arguments of each method during its execution.
Guzzle is a RESTful Web service client framework that enables PHP developers to quickly build testable Web service clients utilizing HTTP/1.1 best practices. It gives you access to advanced features like persistent HTTP connections, parallel requests, exponential backoff, over the wire logging, MD5 validation, cookie jars, and a caching forward proxy.