Makes Gmail™ your default email app (original ext repackaged without toolbar button, with safer links & working 'copy address')
Makes the Gmail™ webmail your default email application.
You can also add an "Email this" command to the right-click menu. Ctrl-Shift-M will open Gmail to send the current page. These can be configured in the options pane.
Note: You might need to reload Chrome for the extension to get effect.