There are many similar frameworks to choose from. Such as: (in no particular order) GWT (http://code.google.com/webtoolkit/ http://code.google.com/webtoolkit/)

There are many similar frameworks to choose from. Such as: (in no particular order) GWT (http://code.google.com/webtoolkit/ http://code.google.com/webtoolkit/) SmartClient (http://www.smartclient.com http://www.smartclient.com) NOLOH (http://www.noloh.com http://www.noloh.com) DHTMLX (http://www.dhtmlx.com http://www.dhtmlx.com) QooXdoo (http://qooxdoo.org/ http://qooxdoo.org/) Vaadin (http://www.vaadin.com http://www.vaadin.com) Echo (http://echo.nextapp.com/site/echo2 http://echo.nextapp.com/site/echo2) Servoy (http://www.servoy.com/ http://www.servoy.com/) Sproutcore (http://www.sprotcore.com http://www.sprotcore.com) Sencha (http://www.sencha.com http://www.sencha.com) Each of the above has their strengths and weaknesses, and there are many more frameworks than I can list at the moment, but even with the select list above we can see there are many more contenders in this space than just Cappuccino, Sproutcore, and GWT. Disclaimer: I'm a co-founder of NOLOH [edited for clarity]