Well, I heard someone mention that on twitter, and the javascript does contain the "qx" toplevel object. Don't know if it's heavily modified or not. Also, judging from the page names it's using ASP.NET. Considering that a lot of the usual web games (all those boring fighting sims) are a dreadful hodgepodge of PHP and Flash, this is quite refreshing.

Also, the gmx.com web mail service seems to be written in qooxdoo (and was probably the reason for writing the library in the first place). It's interesting to compare that to the rather dated original European GMX webapp (gmx.net), which seems to be lingering on in a barely modified Perl CGI incarnation.