We present a rendering engine for displaying graphical user interfaces on multiple devices. The renderer interprets a standardized XML-based user interface description language: the User Interface Markup Language (UIML). A generic architecture for the renderer is defined so that deployment of the engine on different devices implies only little effort. We show that our rendering engine can be used on iDTV set-top boxes, mobile phones, PDAs and desktop PCs, and smoothly integrates with both local and remote application logic. As a test bed for the UIML specification we also explore support for extensions to UIML that enable the user interface designer to maximize accessibility and target multiple devices and different types of users at once