It is available for Mac, Windows and Linux. The project started and maintained by Adobe, but it’s not a commercial product.
My favorite feature is divide the window into two parts (both vertically and horizontally), with this options is able to work more than one file at once.
It have a text predicto, while you are typing, Brackets will propose you code elements that fit wiht your input, it very useful.
With the live preview button, Brackets open the current file in Chrome.
For my the best is the amount of free extensions available.