The relationship of ExtJS, GWT and SenCha. The detail information info can be found at Wiki page.

On 15 June 2010, the merge of Ext JS with JQTouch and Rapha?l was announced[7] forming a new organisation called Sencha Inc. Ext JS continues to be available as a main product on the new Sencha website[8] together with Sencha Touch, Sencha GWT (now Sencha GXT), Sencha Architect, Sencha Animator and Ext core.