This is a very old project saved from the Google Code shutdown. It lived at http://code.google.com/p/gwt-maps3
This is a draft set of GWT bindings for Google Maps API v3.
What works today: Maps, InfoWindows (which can include Widgets), Markers, Polygons, Events (for the above)
What hasn't been implemented yet (but you can implement with JSNI): Geocoding, Controls, Polylines, Directions, Elevation, Custom Overlays
There are no official releases, but the code is being actively used. You can checkout the code and build simply with Eclipse and ant.