paxhtml
paxhtml is a bespoke Rust library for declaratively constructing HTML. It provides a JSX-like html! macro and an arena-backed representation for rendering pages. Its primary consumer is this very website.
At the time of creation, the solutions for this were either incomplete or overly complicated (i.e. trying to implement the entire HTML spec). I just needed something ergonomic for use here. Today, something like topcoat's macro would suffice.