TexturePacker - Texture Packer is hands down the best sprite sheet generation tool on the market.
Godot Engine - Feature-packed 2D and 3D open source game engine.
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.
GDevelop - GDevelop is an open-source game making software designed to be used by everyone.
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.
Unity - The multiplatform game creation tools for everyone.