This is an AppEngine app that I wrote in 2012 and use to manage RSVPs for LAN parties.
(I have this, house, see... http://kentonshouse.com)
This app probably isn't useful to anyone other than me.
I used AppEngine mostly because I was a Google employee when I wrote this. Today, I would have used Meteor, and deployed on Sandstorm.
The code is an Eclipse App Engine project (use the Google App Engine Eclipse plugin).
Note that the directory war/WEB-INF/lib/ in the source tree needs to be manually populated with the necessary jar files. The files needed are listed in war/WEB-INF/lib/files.txt -- they should be findable via Google.