Gmail  is available across all your devices Android, iOS, and  desktop devices. Sort, collaborate or call a friend without leaving your  inbox.
Here's over to 10 Gmail Labs features you should enable right now.
Undo send
We've  all been there: You spend half an hour writing a strongly worded  letter, hit send, and realize you probably shouldn't have done that.  Thankfully, Gmail's Undo Send feature — available in Gmail Labs — is  there to save you from yourself.

After sending an email, Gmail will wait a predefined number of seconds  (5, 10, 20, or 30, configurable in Gmail's settings) before sending.  During this period, you can hit the "Undo" button to take back your  mistake.
Even if you don't foresee needing it, it's a lot better  than yanking out your Ethernet cable, so you might as well keep it  around just in case. I use it far more than I'd like to admit.
Custom keyboard shortcuts
We  love keyboard shortcuts. It's no secret. The shortcuts in Gmail are  some of our favorites, allowing you to ninja your way through Gmail with  just your keyboard — and they even add a few every once in a while.

However, if you don't find Gmail's default keybindings very intuitive,  the Custom Keyboard Shortcuts feature — available in Gmail Labs — lets  you customize your own shortcuts from Gmail's Settings page.
Preview external services in messages
Gmail  has quite a few labs that let you preview things like videos,  documents, voicemails, and images in emails if they're sent from certain  services. For example, if one of your contacts sends you a message with  an address in it, the Google Maps Preview Lab will automatically show  you that address on a map.

There are also preview Labs for Google Voice, Yelp, and Picasa if you or your contacts use those services.
Auto-advance
If  you cycle through a lot of messages at once, it's probably really  annoying that Gmail takes you back to the inbox whenever you delete,  archive, or mute a conversation.

The Auto-advance feature, available in Gmail Labs, lets you choose what  Gmail does in this situation, so you can go straight to the next (or  previous) email whenever you delete or archive a message.
It's small, but a good time saver and a fix for a pretty big annoyance.
Unread message icon
Gmail's  tabs might light up when you have new messages, but if you want a quick  glance at how many unread emails are in your inbox, Gmail Labs' Unread  Message Icon will do the trick.

It's perfect for keeping Gmail in a pinned tab, but make sure it  doesn't distract you: after all, you shouldn't be answering email as  soon as it comes in. So if having it on tempts you to constantly check  your inbox, keep it off.
Send & Archive
Just head into Gmail's General Settings and click the "Show "Send & Archive" button in reply" radio button. From now on,
 
when  you're composing an email, you can send your message and archive the  thread in one fell swoop-keeping your inbox clean and tidy.
Apps search
If  you use Google Docs or Google Sites, Apps Search (available in Labs) is  a great feature that extends Gmail's search capabilities to those two  apps. That way, when you search for something in Gmail, it'll also bring  up matching search results from Docs and Sites below the Gmail ones.

That way you can do all your Google-related work in one, consolidated tab.
Default 'Reply All'
Arguably  the most controversial feature of the bunch, this lets you set your  default reply action to "Reply All" instead of "Reply". Often, when  multiple people are involved in an email thread, one person will break  off by accidentally hitting the "Reply" button instead of "Reply All",  and then everyone else misses that part of the conversation.

Save  yourself from being that person by tweaking this option in Gmail's  general settings. On the occasions you want to reply just to one person,  you'll still be able to do so by hitting the drop down menu next to the  Reply All button.
Canned responses
If you  find yourself doing a lot of repetitive typing, the Canned Responses lab  will save you serious time. Enable it in Gmail Labs, type in the  messages you find yourself sending over and over again, and then send  them in the future with the click of a button. You can even send them  automatically using filters, which makes for a useful vacation  responder.

Note also that you can use OS-wide text expansion if you need to do  this outside of Gmail — though Gmail's canned responses can be used no  matter what computer you're on. They're even available on your phone.
Quick links
While  features like starred messages and Multiple Inboxes are great for  accessing oft-needed labels or messages, Quick Links can access just  about anything, right from Gmail's sidebar.

Once  you enable Quick Links in Gmail Labs, you'll see a box on the left, in  which you can add one-click access to any bookmark able URL in  Gmail—including saved searches, specific messages, labels, or anything  else.
You can just use them as a handy grab bag of links, or even turn them into a killer to-do list.