Hacker News Reader

Check out https://github.com/rogerwang/node-webkit/

I think a lot of the apps you are using this, or something very similar. I've only played around with it very briefly, but like jw989 said it's pretty straightforward.

Some tutorials here: http://www.scriptol.com/javascript/ Even PHP can use an HTML interface!

Honestly, if you understand how to build frontend applications it is as simple at creating an index.html file and attaching it to the webkit browser.