Back in the 1999-2000 I developed a multi-channel portal system, where each portlet[1] was emitting an XML with a custom schema, and the backend was transformin

Back in the 1999-2000 I developed a multi-channel portal system, where each portlet[1] was emitting an XML with a custom schema, and the backend was transforming it using XSLT to HTML, WAP/WML and VoiceXML. I think I even had an experimental 3D VR version using Flatland markup language or something like this. Also, at one of the messaging companies we developed an XML-based DSL for messenger-embedded 3rd party app development. It was inspired by Mozilla XUL, and was similar to modern chatbots with UI and WeChat's mini-apps. -- [1] an individual applet-like component in a portal UI