Mozilla Prism is a great open-source program that can create web applications from Mozilla Firefox (add-on). The web app is run like a normal application, using some sort of a toned down version of Firefox.
What is this for? You can create a "Gmail Program" using this, or "Gmail Calendar" program, etc. You can even create a "BleepingComputer" app right on your desktop!
Please note that this is a prototype/beta, there may be some bugs. I haven't found any yet!
To delete the web app, simply delete the shortcut. To uninstall, remove the add-on. A standalone version is also available.