Chris McMacken took the initiative one day to start a repository on github where a bunch of us PHP developers could add our useful bits of code and turn it into something useful and able to be shared with others. There's not a lot of web-based documentation in the repository but this site is here to help.
DB - A database-agnostic abstraction layer designed to create SQL for you.
DependencyInjectionContainer - Help reduce class coupling, singleton use, and duplicate class instantiation code.
Dump - A way to show variables like print_r(), var_export(), and var_dump() but a little more helpful.
Friend - Get at another class's private and protected methods and properties. Great for testing.
Logger - A simple class for logging various types of messages.
Session2 - An update to PHP's session functions.
Tokenizer - A class to consistently format tokenized PHP code and navigate the tokens.
WebRequest - A safer alternative to the $_GET, $_POST, and $_REQUEST superglobals.