For the last few months, I have been using Mozilla Prism to read my (Google) mail. Prism turns web pages into standalone applications so that I do not have to log in to my Google account with my main web browser.

Today I switched to Fluid, which is a Mac-only (Leopard-only, in fact) application that does the same thing, but is more polished than Prism. For one thing, it is more tightly integrated with the Mac: The GMail application it creates is a real standalone native application (works better in the Dock than GMail Prism, which was only a document), it uses Growl notifications and software auto-update, there is a full screen mode, and it can also create MenuExtras (so that you could get the latest slashdot articles in a pulldown next to the battery life indicator). It is based on WebKit rather than Gecko, has a lot of preference panels, and you can write extensions using Greasemonkey-compatible JavaScript or Objective-C. I also had a weird performance issue with GTalk in GMail in Prism (typing into the chat window was painfully slow), that I expect to be gone now.

Update: One problem with using Fluid is that apparently all WebKit applications share the same browser cookie storage (and there seems to be no way to turn that off). This makes it currently impossible to keep login information separate from Safari, and between Fluid applications. Fortunately, I do not use Safari, and Camino and Firefox of course have their own cookie jars. On the other hand, a lot of applications embed WebKit these days, and I am not at all comfortable with the notion that they all potentially leak state and clobber themselves.