Alternatives to browsers

SVG Scalable Vector Graphics viewers offer the opportunity to present more sophisticated presentations than any other markup technology, and compete with Flash to some extent.
SMIL Synchronized Multimedia Integration Language promised a markup standard for managing and presenting multimedia content, but has largely foundered on indifference (and some hostility) from Microsoft and Macromedia.
WAP Wireless Application Protocol is widely implemented in cell phones, and offers developers a way of interacting with users on simple devices. It uses an XML-based vocabulary to transmit information.
VoiceXML VoiceXML offers developers a different way to present their XML information, using voice synthesis and recognition to create telephone or other audio services.
Terminal interfaces Terminals aren't dead yet. You can use XML to generate and manage text-based (and graphics-based) terminal interfaces.