This is the Roo Javasript library - RooJS It is based on a fork of the original ExtJS1 code, and the pre-1.0 resources which where available under a LGPL and BSD licences Quite a bit has changed since the original Fork (see CHANGES.txt it's updated occasionally) In theory it should be API compatible with ExtJS1, however it includes quite a few fixes and better security that ExtJS in general.