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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.

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.

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.

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.

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.

Wick is a free Flash-like browser-based toolkit for creating small interactive things for the Internet. With Wick, you can create games, animations, and everything in between. Your creations can run on any device with a web browser - that means mobile too. And since Wick lives in the browser, you don't have to download any extra software to use it!

An open-source 3D/2D game engine for ObjectPascal.

Platinum Arts Sandbox Free 3D Game Maker is an open source free game maker, free RPG Maker, free sidescroller maker, free Machinima creator, and game design tool that makes it easy for kids and adults to create video games, maps and worlds.

Adventure Game Studio provides the tools to make your own adventure, for free! Bring your story and artwork and slot it in, and let AGS do the rest.

Amazon Lumberyard is a free, cross-platform, 3D game engine for you to create the highest-quality games, connect your games to the vast compute and storage of the AWS Cloud, and engage fans on Twitch.By starting game projects with Lumberyard, you can spend more of your time creating great gameplay and building communities of fans, and less time on the undifferentiated heavy lifting of building a game engine and managing server infrastructure.

ENIGMA, the Extensible Non-Interpreted Game Maker Augmentation, is an open source cross-platform game development environment derived from that of the popular software GameMaker. Its intention is to provide you with a quality game creation tool and a bridge between high- and low-level programming languages. It can be used either through an IDE, namely, its sister project, LateralGM, or through a Command line interface.