There are several cross-platform, open-source HTML/CSS/JS desktop
frameworks available. The most popular, in descending order:

"The Electron framework lets you write cross-platform desktop applications
using JavaScript, HTML and CSS. It is based on Node.js
and Chromium and is used by the
Atom editor and many other
apps."
- Actively developed by GitHub

"NW.js (previously known as node-webkit) lets you call all Node.js modules
directly from DOM and enables a new way of writing applications with all
Web technologies."
- Has custom APIs (Node plugins) for building UI
- Sponsored by Intel

"Chromium-based cross-platform / cross-language application framework.
Thrust is require/import-able, it lets you distribute NodeJS, Go or Python GUI apps directly through their native package managers."
- Language bindings allow you to use Node.js, Go, Python, or Scala as the backend

"A framework for building native-quality HTML5 apps that work everywhere.
Use Enyo to develop apps for all major platforms, from phones and tablets
to PCs and TVs."
- Bundles everything into a package for installation.
- Developed by LG
See also: