Atom editor (or just Atom) is free and open source text and code editor build by GitHub. It is build using Chromium, nodejs, CoffeScript and Less. There are few other editors build using nodejs, second most popular project is Brackets. I've tried both and found Atom stable among two. Another advantage Atom has more plugins than Brackets. Recently I'm started to using it as alternate for Sublime Text.
It has many plugin for Drupal also. I'm using following plugins