XPages
XPages is a server-side web application framework developed by IBM for building dynamic, data-driven web applications on the IBM Domino platform. It uses a component-based model similar to JavaServer Faces (JSF) and allows developers to create rich internet applications with integrated access to Domino databases. XPages applications run on the Domino server and can be deployed to web browsers or mobile devices.
Developers should learn XPages when working with legacy IBM Domino applications or in environments where Domino databases are the primary data store, as it provides a modern web interface for these systems. It is particularly useful for enterprise applications requiring rapid development of collaborative tools, forms, and workflows that integrate with existing Domino infrastructure. However, its relevance has declined with IBM's shift away from active development, so it's mainly for maintenance or migration projects.