PHP DBTreeView is a useful Ajax web control to display a treeview. This component is designed to extract dynamic content from database, so that the tree content is updated step by step. You don't need to know JavaScript to use this tool. (R. Cardon)
JQTree4PHP is a PHP library that allows the creation of an expandible tree of items ( treeview ) in an easy way and totally directed to objects (OOP) to be used in User Interfaces, implementing the JQuery javascript library and its plugin jQuery.treeview
TafelTree is a treeview in javascript. The structure of the tree is described in JSON format. It supports lot of options and user functions, just like the commercial trees. It's supported by all major browser (mac, linux and windows)