clonefish - PHP form generator and validation class
Clonefish is a PHP class, which helps creating web forms using a simple configuration file. In fact, it sounds a piece of cake - but this class also performs various client- and server-side validation for the inputs, has ADOdb database integration for dynamic controls (eg. options of a select created from rows of a database table), multilanguage support, tree-structure select controls, and more! I've already used it to build number of applications, so I feel it a mature and proven technology right now.