One of the most important endeavors in the PHP universe is the PHP Framework Interop group. The group consists of several maintainers of big PHP projects. Their aim is to find commonalities between their projects and find ways to work together. They do this by proposing and accepting PSR's, short for PHP Standard Recommendation.
One of the most important PSR's is PSR-4 (and the now deprecated PSR-0) which describes a way to autoload classes. Thanks to this standard packages can be easily be reused in many frameworks and projects. PSR-2 is another important one. It is a coding style guide and greatly improves readabiltiy of code when working with a bunch of developers. There are several other PSR's that have been accepted.
Today PHP-FIG published their new site. It features a beautiful design by Jonathan Reinink (he's the designer of the PHP League sites, author of Glide, and creator of the PHP Package checklist). If you use PHP in any way you owe it to yourself to check it out the new site.