Hello,
Do you plan to realesed dhtmlxToolbar under GPL license ?
I would like build a GPL software with dhtmlxGrid, dhtmlxMenu, dhtmlxTree and dhtmlxToolbar but I can’t because dhtmlxToobar’s free license is not compatible with GPL license
Thanks for your answer 
Please contact our sales department - sales@dhtmlx.com - I think it will be possible to made exception in your case.