1. Unsubscriber for Gmail (free, iOS) is the quickest way to unsubscribe from newsletters and mailing lists.
The app will scan your Gmail account for any email lists you may be signed up for. All you need to do is swipe left to unsubscribe and swipe right to stay subscribed. It's a super-quick and easy way to clean up your inbox!
If you don't have an iPhone, scroll down to "Websites and Skins" for a browser-friendly unsubscriber!
With one swipe, you can archive, delete, or schedule an email to show up at a later time. With one tap, you can add an attachment from Dropbox, Google Drive, or OneDrive. Outlook's killer feature, however, is that you can view your Google Calendar and Google Drive (or OneDrive or Box) files without ever leaving the app.
3. Mailburn (free, iOS) turns your Gmail threads into chats.
4. Mailpilot ($20, Mac) is a beautiful desktop Gmail client that treats emails like tasks.
5. Gmail Offline (free) allows you to read, respond to, search, and archive mail without internet.
6. Gmail Mail Checker displays your number of unread messages.
7. With Boomerang, you can schedule emails to be sent at a later time.
8. Ugly Email checks if your email is being tracked.
9. Send self-destructing email with Snapmail.
10. The Gmail Menu extension for Safari gives you a shortcut for emailing links.
If you email links often, consider getting this Safari extension, which adds a "Gmail" shortcut to the right-click (or control + click) menu on Mac. You can select "Gmail" on any page to open a new tab or window with an email already composed. The subject is the page title and the body is the URL.