wxWidgets - wxWidgets: Cross-Platform GUI Library
Svelte - Cybernetically enhanced web apps
Electron - Build cross platform desktop apps with web technologies
Glimmer - Fast and light-weight UI components for the web
GTK - GTK+ is a multi-platform toolkit for creating graphical user interfaces.
Preact.js - Preact is a fast 3kB alternative to React with the same modern API. Components & Virtual DOM.