Fluid allows you to create individual apps from practically any web page.
For example, you can create an individual SSB (Site Specific Browser) for Twitter, Facebook and GMail. Fluid will build the SSB and place it nicely amongst all your other apps. Launching the app produces its own separate SSB window with its own functions, such as 1Password support and also a full menu bar and preferences, just like a full app.
You can also easily customize the favicons (which are automatically pulled from the original site when you create a SSB) and use your own images. You can find quite a few here on Flickr to get you started.
Twitter as a SSB
Custom icons for GMail and Twitter
(check out the hard sell at the last 30 secs of the video its quite funny! 
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Head over to Fluid and check it out for yourself.
