Question

Sometimes I think I want to develop a standalone (needing neither a web server nor a browser to run) desktop GUI application for Windows, Mac OS X and Linux using HTML5, CSS and JavaScript to form the GUI.

But as far as I know, both Adobe AIR and Mozilla Prism are deprecated. What are other options for this task?

UPDATE: Responding to the answers and comments already got, I’d like to emphasize that the applications must work on Windows, Mac OS X and Linux without any serious modifications. The platform is to be actively developed and supported for all the 3 major PC OSes. Single-platform applications are not an option, neither are applications with limited support of one of them.

Answer 1

Based upon the solutions evaluated on http://blog.neamlabs.com/post/36584972328/2012-11-26-web-app-cross-platform-desktop-distribution, these should be the most relevant HTML5 Runtimes with regards to your requirements.

• XULRunner – Benefiting directly on Firefox development efforts, this is an extremely well-maintained solution with great cross platform support but with almost non-existant tooling or documentation for packaging and distribution other than those of Firefox and other open source XULRunner-based applications themselves
• Chrome Installable Web Apps – Like a Chrome web app with more desktop integration. No flash support.
• Mozilla Native Web Apps – Like a Mozilla Open Web App with better desktop integration. Still requires online installation through Firefox Marketplace. 
• TideSDK (formerly Titanium Desktop) – Although it may appear to be the perfect solution all-round, the current state is that TideSDK is not nearly production ready (may change in a couple of months or so, due to active development)
• node-webkit looks very relevant, not sure about the “production-ready” part though.