This extension is the very popular, with over 800,000 users recorded by Google. Checker Plus for Gmail notifies you of new emails with pop-up windows, which show a preview of an email’s first few lines, in the lower-right corner of your OS’ desktop. By clicking its icon in the Chrome extensions toolbar, not only can you glance through first-line previews of your new emails, you can do most email management functions without ever needing to open the Gmail main page. You can even compose a new email directly from the extension — again, without having to go to the Gmail main page. The settings to adjust the UI of Checker Plus for Gmail are many, and intimidating to go through. Fortunately, its default settings will probably satisfy most of your needs.