Mozilla just released a very nice tool to help bring web based applications to the desktop.
Mozilla Labs Blog » Blog Archive » Prism
Naturally, the first application I tested was Zimbra. I'm toying with the idea of migrating some of my end users who refuse to use the zimbra web app, simply because it's a webmail instance. There's a stigma that's associated with webmail and the assumption that it's not as powerful as Outlook.Prism is an application that lets users split web applications out of their browser and run them directly on their desktop.
I tested Zimbra Desktop, but in my evaluation, it's not ready for my users yet. Prism, however was very fast and uncluttered. It allowed me to make use of Alt-Tab and it had the appearance of a stand alone application.