Playing with TiddlyWiki in my browser the other day blew my mind because it was saving things to my computer, even though I didn't have a web server or database running locally. That's the first time I've ever seen that and it hurt my brain! I've gotten used to my browser making calls to the network and back, having an app not do that was nutty. But after reading up on the HTA stuff again, I thought - hey, this would be perfect for TiddlyWiki - and within 2 minutes, I had the "app" running with it's own spot in my task-bar and ability to save and everything. All that separates an .hta file from a normal .html file is the file extension (obviously) and an hta:application tag you put in the header. That's it. So I just "made" a few apps from stuff online - TiddlyWiki is the only real client-only app, the other two are just wrappers around normal web pages... but they're all pretty neat to play with.
So there's lots of interesting things you can do with this, no? All those next-gen Calendaring apps, for example? Imagine if instead of always having to be online, you can use this sort of thing offline and be able to sync when you're connected later. Lots of stuff like that comes to mind. Though there are definite limitations without signed apps - I quickly discovered that trying to use the XMLHTTPRequest object with a dynamic URL prompts the user every time, which is defniitely annoying. And, hey, if you didn't know, I also discovered that Microsoft has a patent on the HTML Desktop app already. Isn't that nice?