The "hidden gem" of browser development

Qooxdoo has been powering desktop grade applications for over 10 years. Originally started by 1&1, Qooxdoo transformed into an entirely community lead Open Source project, operated by a non-profit foundation and is entirely based on the MIT license. Qooxdoo has an incredibly stable API, with backwards compatibility a primary goal, hardly anything needs an update except when browsers change in backward-incompatible ways.