The source code is released under Apache License, version 2.0 and available on Google Code Hosting. The url is http://code.google.com/p/blogspot-on-appengine/
The following command can be used to check out the latest project source code (all in one line):
svn checkout http://blogspot-on-appengine.googlecode.com/svn/trunk/ blogspot-on-appengine-read-only