Lozad.js - Highly performant lazy loader in pure JS
TexturePacker - Texture Packer is hands down the best sprite sheet generation tool on the market.
Dragula - A drag and drop library for developers
Free Texture Packer - Free Texture Packer is an open source tool that allows you to pack multiple images into one atlas for you games or sites.
JSconsole - Load external JS libraries in your favorite console
Sprite Sheet Packer - Sprite Sheet Packer is online that you can easily use to pack sprite sheets, including data formats for CSS, LESS, and Phaser.