As Paul Jones mentions in this new post to his blog the Aura project, a PHP framework, originally targeted at PHP 5.3 has changed its direction a bit - they've shifted from a focus on PHP 5.3 to the upcoming PHP 5.4 release.

When I initially announced the Aura project, it was targeted at PHP 5.3. With a stable release of PHP 5.4 impending, we have moved the target to PHP 5.4. In addition, we have made 1.0.0-beta1 releases of almost all the component packages. (See an earlier announcement from Hari KT.)

The components include: a dependency injection container, an autoloader and a view system that are all self-contained with no other dependencies. You can find the complete code for these containers (and one for combining them all into a single system) on the project's github page.