Atom is an editor released by GitHub originally for Mac OSX. Their official website is Atom.IO and you can find out more information there. Atom is similar to Sublime Text, the editor is fully customizable just by editing the HTML, CSS, and Javascript, making it easy to build packages for.

Disclaimer: I am unaffiliated with GitHub, these builds are provided at your own risk, although a lot of people are using them now (Just Google atom builds for windows). Attribution: Atom, and the Atom logo are owned by Github. Both are licensed under the MIT license allowing me to display them here under terms that I attribute the original author(s).