Editor's Choice :

Visual Studio Code (Win, Mac, Linux)

De facto choice

Atom (Win, Mac, Linux)

Simple, user-friendly, and customizable

Brackets (Win, Mac, Linux)

Made for web design

Repl.it (Web)

No download or signup required

CodePen (Web)

Front-end playground

Codeshare (Web)

Like the Google Docs of coding

Nano (Mac, Linux)

Edit in the shell

ALTERNATIVES :

Notepad (Win) / TextEdit (Mac)

Barebones and Built-in

Sublime (Win, Mac, Linux)

Feature-packed, better for large projects

VIM (Mac, Linux)

Steep learning curve, extreme productivity

Emacs (ALL OS)

Steep learning curve, extreme customizability

Spaceemacs (Win, Mac, Linux)

VIM + Emacs

Notepad++ (Win)

Amped up Notepad/TextEdit