This is a Chrome App that wraps around Draft (https://draftin.com/), an online application to help you write better. Why a Chrome App when Draft is already available from a web browser? Because a Chrome App + Chromes App Launcher adds a few extra niceties to Draft that you cant get just from your browser. For example, you can now access Draft from OSXs Spotlight and CMD+Tab. Note: This is still Draft in online mode. You can fool with offline Draft in Settings->Labs, but this is still predominantly the online version of Draft, just wrapped in a Chrome App.
You can Follow the below Step By Step procedure to install the Draft Chrome Extension to your Chrome Web browser.
It is the Draft Chrome extension download link you can download and install Chrome Browser.