It's called Google Brackets.
I haven't seen it mentioned in this forum before. I tried it today and it is really nice. Not advanced (yet..(still in beta mode)) like a lot of other text-editors but, like all of Google's products, emphasis is on user experience, simplicity, and ease of use.
It also has a live preview mode where changes you make are visible instantly in your browser. But for some reason, that is not working for me.