A WordPress transients interface with support for soft-expiration (use old content until new content is available), background updating of the transients (without having to wait for a cron job), and a chainable syntax that allows for one liners.

A no-frills PHP forum app. Nice!

"Hierarchical MVC". Sounds like it supports multiple apps in the same system, like Django.

Exact and full port of the Django template language for PHP.

A PHP template language inspired by Django.

Apache, MySQL, PHP in a box.

Video tutorials for the PHP MVC framework

Live as-you-type regex helper so you get your matches right.

A good starting point.

YES!

Handy.

Another CSS compiler, this one in PHP.

A PHP function-level profiler.

Decent alternative to phpMyAdmin?

...works outside of CodeIgnitor too.

"SimpleMC is meant to provide an easy way for content editors to edit blocks of content. It is meant for smaller sites, where clients just want to get in, edit some content, and get out."

RadientCMS ported to PHP. Nice.

Looks fairly professional

Google gives low-level best practices and high-level concepts on how to create a fast web app.

Decent-looking eCommerce software from this decade. It's distributed under an Open Software license (doesn't look as open as GNU or MIT). Has a plugin architecture and is bundled with an iPhone theme.

The php5 script that strips and gzips a collection of CSS and JS files, speeding up HTTP requests enormously.

For when you want to *just* use .htaccess

Clean URLs with mediawiki

Allows you to use a replacement syntax parser, like the markdown or textile library for your mediawiki install.

CSS pre-processing, server-side importing, constants, and more, thanks to Shaun Inman and the magic of PHP + apache.

Make your pages load faster by combining and compressing javascript and CSS files with a simple PHP script and a tad bit of URL rewriting.

Shaun Inman

Paul James rocks the party. Favicon + Avatar = Favatar.

Bills itself as a CMS/PHP applications framework, and as an "AJAX" CMS. Not sure what that is, but the clean URLs and XHTML are promising.

Like the famous styleswitcher.js, only it doesn't rely on client side scripting being enabled, and refreshes the page to accomplish the CSS switch.