HTML 5 applications in the browser really seem to be taking off. I've been using src:kit within Google Chrome for a few weeks and love it. I'm an ASP.Net (C#/MVC 3) developer by trade, and in the past did several pieces of WebForms programming.
With Windows 8 app development moving into the trade of local HTML5 apps, and the major smartphone browsers supporting HTML5 installation, as well as many platforms supporting it (PhoneGap and Titanium, for example), are we already/will we soon be at the point that I could create an app that would be fully "installable" to run as a standalone on every platform?
I do realise that a database (or instert-your-data-store-here) would also be necessary, so adding another language in there for middleware would be necessary. C# on Mac/Linux with Mono is possible, but Mono generally only creates a GTK+ Application, so I would likely need to create another wrapper to house the application... I think.
Any suggestions of a better language to use as middleware? I.e. for ease of transportation - I've got far more experience with C# than anything else so would like something from that family if I'll need to do something different.
Basically, how far away are we from this? What still needs to change? Most importantly, if it is possible (which I believe, theoretically it is), what is the big jump between where we are now and when we will be there?
This will eventually turn into a program, so it is a completely practical problem that I'm working my way through (I'll start development after Christmas).
EDIT: To clarify, by 'every' platform, I include at least the following: Windows XP+/Mac OS X/Linux: any distro pretty much in the last 2 years/iOS/Android/Blackberry 5+/Windows Phone 7+