Electron is a framework for building desktop applications using JavaScript, HTML, and CSS. By embedding Chromium and Node.js into its binary, Electron allows you to maintain one JavaScript codebase and create cross-platform apps that work on Windows, macOS, and Linux — no native development experience required.
Electron is so much more than "just a web engine with a full set of OS xalls hooked in". Ultralight and Sciter are frameworks that actually just happen to use HTML, CSS and JavaScript for UI development. They aren't fully-fledged web browsers without a search box, they are tailor-made for app development.