So. You've gotten the message that multitasking is bad, that email is satan-spawn, and that you should give yourself some uninterrupted time to work. You dutifully sit down at the computer. Email alerts are off. Web browser is closed. And you start to write (or draw, or code, or dream, or whatever it is you do that creates value). And then you suddenly remember: you have to remind your wife to pick up the rhinestone-studded gerbil collar from Petsmart. It's just a quick email; no big deal. It'll take JUST A SECOND. You toggle over, write the email, and are about to go back to your work when you think that you ought tell your boss to follow up with HR about the travel expenses. So you write that, too. It only cost you another 60 seconds.
Then you see them: eleven new emails. And being an animal (bipedal, yes; opposable thumbs, yes -- but still an animal), you can't resist getting distracted by shiny (or bold) objects, and you read them. And respond. And respond to the next batch of messages that come in while you're in email. Before you know it, you've disappeared down the electronic rabbit hole. For 45 minutes.
This happens all the time with email and with web browsing. Maybe you need to quickly check Napoleon's height (5'6" or 5'7") or make sure that you when you referred to Monet, you didn't mean Manet. You get sucked into the vortex, and next thing you know, you're reading about Edward Tufte, Hitler's error in opening a second front in Russia, and the roots of Impressionism. And another 45 minutes vaporizes into nothingness.
Here's the thing: it's not enough to block out the externally imposed interruptions. You also have to guard against self-inflicted interruptions. These are sneakier, more prevalent, and more damaging than you think. It may be (relatively) easy to tell your colleagues or clients that you only check email three times per day, but it's not so simple to tell your brain to stop remembering stuff to do. Or to turn off your curiosity. Without realizing it, you're your own worst enemy.
The solution is refreshingly low-tech -- you do not need an app for it. Keep a pad of paper next to your computer as you're working. When you think of something that you have to do (make a phone call, send an email, get some information on a prospect, etc.), scribble a note to yourself on the pad and KEEP WORKING. Don't break your momentum. When you're done with that task or project, then you can follow up on the items on your note pad.
You're essentially making a holding pen for random to-dos so that you can free your brain to focus on the real work you have to do. You'll be amazed at how much less distracted you feel and how much more productive you become.