WriteNext - The writing application that boosts your writing. Increase focus and writing performance and reduce distractions by separating your creative writing from other activities. Let writing be the only activity you perform in the writing application.
Cold Turkey - Cold Turkey is a free productivity program that you can use to temporarily block distractions so that you can get your work done!
Calmly Writer - Distraction-free text editor for Mac, Windows, Linux and ChromeOS.
Stay Focused - More suitable with Google Chrome, this service enables you ensure you do not waste precious time on updating Facebook status or chatting with people.
Stashany - Online notepad for developers
Freedom.to - Freedom is a productivity hack that lets you block apps, websites or the entire Internet on iPhones, iPads, Windows and Mac computers.