Facebook used something called Primer that very similar to HTMX. It was widely used until about 2010 or 2011. It slowly replaced by JS doing ad hoc DOM manipula

Facebook used something called Primer that very similar to HTMX. It was widely used until about 2010 or 2011. It slowly replaced by JS doing ad hoc DOM manipulation as engineers strove to build more sophisticated interactions, and the React was developed as a way to manage the complexity of handling updates over time.