Hmmm... a virtual machine for HTML5/CSS/JS... sounds like a browser. :)
Maybe Adobe AIR would do the trick, because it's based on the idea of bringing rich Internet apps to the desktop. I've never used it, however.
One thing you could do is develop a very basic desktop app that uses some kind of prepackaged web browser control (e.g. if you're developing for a Mac, just drop a WebView in the window and add some basic code to load your html upon app startup).
