This is a small chat app built on Google App Engine. It also allows interactions from an XMPP client and file sharing.
It's very simple, so you should look at the code. It uses several of Google App Engine's awesome APIs, and was our submission to the "Last Call" challenge for GoogleIO 2011. We'll see you there :)
Feel free to fork it, and run under your own Google App Engine account to avoid hitting their "Quota" limits.
Dear Google App Engine team, add a "fork" button in these apps, so I can automatically fork and run under my own account if allowed by the owner of said app!