Over the years, the World Wide Web has evolved from a document distribution environment into a rich development platform that can run compelling, full-fledged software applications. However, the programming capabilities of the web browser – designed originally for relatively simple scripting tasks – have evolved organically in a rather haphazard fashion. Consequently, there are many ways to build applications on the Web today. Depending on one’s viewpoint, current standards-compatible web browsers support three, four or even five built-in application rendering and programming models. In this paper, we provide an ”underview” of the built-in client-side web application UI implementation technologies, i.e., a summary of those rendering models that are built into the standards-compatible web browser out-of-the-box. While the dominance of the base HTML/CSS/JS technologies cannot be ignored, we foresee Web Components and WebGL gaining popularity as the world moves towards more complex and even richer web applications, including systems supporting virtual and augmented reality.