Unity!

Godot is a fully featured, open source, MIT licensed game engine. It focuses on having great tools, and a visual oriented workflow that can export to PC, Mobile and Web platforms. It is a cross-platform 2D and 3D game engine and game development IDE.

Unreal Engine is a professional suite of tools and technologies used for building high-quality games across a range of platforms. Unreal Engine’s rendering architecture enables developers to achieve stunning visuals and also scale elegantly to lower-end systems.

GDevelop is an open source game creation software, allowing to make games for the web (HTML5) or for Windows and Linux. No programming or coding skill is required! It is easy to use and powerful enough for advanced users.

Scirra Construct is a 2D game development engine with a focus on building games visually. No programming is required though the software uses a visual method for event handling that relies on programming concepts like variables, loops and conditions. It provides a powerful form of scripting that's as easy as clicking, dragging and dropping.

Polycode's core is written in C++ and currently runs on Mac, Windows and Linux with iOS and Android support planned in the future. All platform-specific functionality is abstracted into a cross-platform core and implemented natively on each platform, so the same C++ code will compile on each supported platform out of the box.

Stencyl is the creator of StencylWorks, a tool that has enabled creators of all all skills levels create iOS and Flash games in no time. In 2012, Stencyl will expand into Android and HTML5 game publishing.

Achieve your Vision using our cutting-edge, 100% royalty-free technology!

Torque 3D is a easy-to-use game creation platform. Architected from the ground up for maximum flexibility and performance across a wide range of hardware and built upon the Frontline award-winning Torque Game Engine Advanced, Torque 3D comes equipped with a full suite of tools and APIs to get your game to the finish line, no matter what your goals. Add publishing paths to PC, Mac, Xbox 360, Wii, iPhone, and the web, and you have the power to distribute games almost everywhere they are played.

Superpowers is an HTML5 development environment for making 2D and 3D games.It can be extended with plugins and lets you collaborate in real-time.

Urho3D is a lightweight, cross-platform rendering and game engine implemented in C++ and released under the MIT license. Greatly inspired by OGRE and Horde3D.

Continuing the legacy of Mark Overmars' Animo and Game Maker, GameMaker: Studio is a proprietary game-creation system which can export to multiple platforms including Windows, HTML5, Linux, iOS, Mac and Android.Often considered the fastest and easiest-to-use cross-platform game IDE technology, GameMaker: Studio allows developers to create games in a single codebase and then publish them to run natively across a wide number of mobile, desktop, and web platforms.

cocos2d-x is a cross platform open source free 2D game engine for mobile gamedev, that is fast and stable, easy to learn and use.

Appcelerator Titanium, offered for free by Appcelerator, lets web developers use web technologies, open source and cloud computing to build native apps for iPhone, Android, Windows, Mac OSX and Linux.

Buildbox is a breakthrough game creation experience. Creating games is as easy as dropping images into the software, making changes to their properties and hitting play.