DHTMLX Ajax Toolkit
DHTMLX components support the main types of functionality required for development of modern Web applications: drag-n-drop (also available between different components, e.g. from Grid to Tree), in-line editing, clipboard operations, special techniques for handling large datasets, powerful script API, built-in client-to-server communications, wide range of client side events, XML/CSV/JSON support (while XML support is more advanced, JSON, as well as CSV, support is also available for most operations).
DHTMLX components are distributed for free under GPL (Standard Edition) as well as on commercial basis (Professional Edition).
More info can be found at; http://dhtmlx.com
Sender; Ivan Petrenko