I wish to create a GAE application using python, however i fear that Google would be the only company in a position to host the code. Can you really operate a GAE application on the private server or any other host?
(Observe that an earlier version from the question improperly known to GWT).
Presuming that by GWT you mean GAE (GWT is perfect for Java and anyone can serve it), appscale is most likely the easiest method to host GAE programs anywhere you would like (including on Amazon . com EC2 and in your data center). Anyone can also begin a business supplying GAE service with AppScale (on Amazon . com, their very own data center, or whatever), which can be attractive for more compact applications (that do not warrant many EC2 or devoted servers). Anyway, because of AppScale and other alike efforts, you certainly do not need to fear "that google would be the only host to host the code".
GWT could be offered by anybody, after compilation it is simply a lot of .js files a GAE web application could be offered only on Google's servers.
The API is public, and also the developer's SDK works and it is OSS however i don't believe it might be an appealing platform for any real company. OTOH, based on the Google Code GAE SDK project it is the same infrastructure they will use but it is tough to beleive the backends accustomed to run without GoogleFS, BigTable, MapReduce, etc. might be as scalable as their own...