Pixelbox.js
A combination of an editor and a simple JavaScript library to create game without the cumbersome aspects of HTML5 development
  rot.js
A set of JavaScript libraries, designed to help with a roguelike development in browser environment
 
Bitsy
A little engine for little games, worlds, and stories
 
CopperCube
A complete 3D authoring tool which includes all the features you need for creating games for multiple platforms
  Isogenic
HTML5 2D and isometric scenegraph-based game engine written entirely in JavaScript
 
KaboomJS
A Javascript game programming library that helps you make games fast and fun.
 
Next2D
An engine that provides a WebGL 2D rendering, a web authoring tool for animation production, and a framework to support team development
  Octo
A high-level assembler for the Chip8 virtual machine, complete with an environment for testing programs, and tools for sharing your creations
  Pixel Game Maker MV
An engine that allows you to build up your own action game with no programming knowledge necessary
  Puzzlescript
An open-source HTML5 puzzle game engine
  Quadplay
A fantasy console by Shmuel and Morgan at CasualEffects for creating and playing retro-style video games on any device.
 
QX82
A tiny Javascript single-library engine that lets you create games and experiences inspired by the look and feel of a retro 80s computer
 
Wick Editor
A free, open-source tool for creating games, animations, and multimedia projects
  Yami RPG Editor
Yami RPG Editor is specially designed for making ARPG