We (Emitrom) just announced Lienzo, which allows your mobile app to work on all devices that support canvas. Web-kit's fragmentation has been a major pain point, and now with Lienzo that pain-point is gone. Lienzo bears an Apache 2 license, so it is gratis.
Lienzo is a pure GWT implementation of canvas. Pair it with our Cordova binding and you can develop canvas-based mobile apps; then turn around and deploy it using Air4j and your app is now a desktop-based app; or run it on the web, out of App Engine like our examples do.
We are in alpha right now; working hard to get more features in. With Lienzo, your imagination is the limit.
http://www.dzone.com/links/javas_future_lays_in_lienzo.html
Full disclosure: I'm co-founder @ Emitrom.
Co-Founder, Emitrom LLC
Bringing Java APIs to the world of iOS, Flex, Touch and more.