Is there a production-ready cross-OS desktop HTML5

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

Opera Widgets is also of the kind you are looking for and is also deprecated, but can be turned on in opera:config as far as I know.

Answer 2

One option is to use berklium. It wraps all the nasty chromium stuff and makes it easier to embed browser functionality in your apps.

Answer 3

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.

Answer 4

There's always Microsoft Silverlight (which does have implementations for Linux/etc. if you're concerned about that, as noted on the linked page).

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Wait a minute, from what I can tell Adobe AIR is still being developed, with a stable release just this past month. It's only Linux that isn't getting official releases anymore, for some strange reason.