FIG¶
FIG is the Framework Interoperability Group. It is ‘moving PHP forward through collaboration and standards.’.
In particular, it discusses, writes and publish PSR: PHP Standard Recommendations. They are currently numbered from 1 to 22, which some retired numbers.
Famous PSR include : 12 (Extended Coding Style Guide), 16 (Simple Cache), 18 (HTTP client).
See also PHP-FIG home
Related : PHP Standards Recommendations (PSR)