Interesting PHP Extensions. These aren't necessarily good to use right off the shelf, but serve as inspiration for things that could be built.

extensions.md

Language extensions

• AOP - Aspect-oriented programming in PHP - http://aop-php.github.com/
• PreProcessor - macro-style processing - http://pecl.php.net/package/PreProcessor
• Meta - AST building from PHP Source - https://github.com/flavius/phpmeta/
• Runkit - Black magic for PHP - https://github.com/zenovich/runkit
• scalarobjects - Register methods on PHP scalars - https://github.com/nikic/scalar_objects

Structures

• Weakref - weak reference implementation in PHP - https://github.com/colder/php-weakref
• xrange - iterator implentation of range (not necessary in 5.5) - http://svn.php.net/viewvc/pecl/xrange/
• quickhash - fast sets and hashes - https://github.com/derickr/quickhash
• pthreads - threading implementation - https://github.com/krakjoe/pthreads

Facilities

• automap - fast map-based autoloader - http://svn.php.net/viewvc/pecl/automap/
• uploadprogress - allow streaming uploads, ability to provide feedback to users - http://pecl.php.net/package/uploadprogress
• igbinary space-efficient replacement for php serializer - https://github.com/igbinary/igbinary/
• phalcon MVC framework with a bunch of builtin things (autloading, caching, routing, etc) - http://phalconphp.com/