Hermes
The Hermes expansion for ExpressionEngine is a collection of PHP and JavaScript classes and functions that will standarize and improve your building of Add-Ons for ExpressionEngine. Developed by Solspace and used by many of its most popular Add-Ons, it will transform the way you develop.
The Hermes folder loads into your 'system' folder right alongside 'dictionary', 'extensions', 'fonts', &c.
NOTE: This Add-On requires ExpressionEngine 1.6.8+, PHP 5+, and MySQL 4.1+.