Here’s quick list of noteworthy community developments for App Engine mentioned below:

-web2py Python framework now supports App Engine, is a "free and open source full-stack enterprise framework for agile development of fast, secure and portable database-driven web-based applications”
-Alternative datastore backend “bdbdatastore” for App Engine applications released
-Earth Hour 2009 site hosted on App Engine
-App Engine supports White House town hall meeting

More info: App Engine blog