Bubbles turns web apps into desktop apps
When you first run Bubbles, you'll see a list of web sites which you can open with the application. You can also add any page you want just by entering the URL. You can start a web app by clicking the "Go" button and you should see icons for each application pop up in your Windows system tray. Click on one to bring up the web app of your choice. Clicking the X bar doesn't close the window, but minimizes it to the system tray. In order to really close a window you'll need to right-click on its icon and select close.
Bubbles appears to use less memory than Firefox when accessing some web pages like Gmail or Yahoo! Mail. But we noticed a window running Google Reader quickly grew to use 50MB. Overall Bubbles seems like a slick and easy to use alternative to Mozilla Prism. But there is room for improvement. For example, when you click on a link in a Bubble window, instead of opening a new Bubble, the program opens your default web browser, which sort of defeats the purpose if you want to do anything besides read web pages.
Bubbles has actually been around a lot longer than Prism, but it works pretty well with modern web applications and supports Greasemonkey. There's even a Gmail notifier that works even with the newer version of Gmail.
[Thanks Jim Mauro!]