mgwt & gwt-phonegap
mgwt is a library for developing mobile apps and mobile websites in GWT from one code base. mgwt provides native looking widgets for many platforms, animations and many other things that you need for writing mobile apps.
With mgwt and gwt-phonegap you can deploy your GWT apps into any app store or let your users use them as a website. Both projects are available under apache 2.0 license from maven central.