- http://trends.builtwith.com/websitelist/Google-Web-Toolkit - but this might be seriously underestimated, as they are not able to detect services accessible after login, where GWT is mostly used.
- http://ars-codia.raphaelbauer.com/2011/12/why-google-web-too...
Other that I'm aware of:
- https://www.cloudorado.com/
- https://ruxit.com/ - their service once you log in
- http://gogrid.com/ - again after login
- Angry Birds web version
- web mail at http://wp.pl (one of the major mail services in Poland)
- Angry Birds web version
- web mail at http://wp.pl (one of the major mail services in Poland)