Writing large desktop-like web applications is a challenge. Adapting such an application to different markets, languages or brands is even more of a challenge. This talk shows how the open source JavaScript framework qooxdoo can be leveraged to build such a rich internet application. As a real-life example the free web mail client gmx.com is used. This talk discusses the development model, customization and deployment of such an application. Learn how JavaScript applications of this size and complexity are fundamentally different from classic web applications, and what issues come up when building fast, multi-language, multi-brand JavaScript applications.