If you use Gmail on a Mac, you should definitely know about Mailplane. It's basically a really fancy site-specific browser for Gmail, getting Gmail out of your browser tab and adding a lot of features you'd demand in a desktop email client. You can drag and drop attachments and sign in multiple accounts at once, just to name a couple. Plus, a release candidate for Mailplane 2.0 just came out, and it adds 37 new features.You can do anything in Mailplane that you can do in Gmail, including the new video chat feature. The new gmail themes are also supported, and you can add your own custom stylesheet. It feels strange to use Gmail in a browser again after playing with Mailplane. Customizable keyboard shortcuts, dragging and dropping, and iPhoto integration are just a few of the handy features that make Mailplane a joy to use. It also supports one of my personal favorite things, Growl notifications
