LITIengine

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MonoGame

Godot is a free and open-source 2D and 3D, cross-platform, game engine released under the MIT license. With Godot, you can develop games using Go or GDScript. Godot provides a huge set of common tools for game production, so that you can focus on making your game without reinventing the wheel. The development environment runs on multiple operating systems including Linux, macOS, and Windows and can compile games for PC, Mobile and the web browser.

Unity is a cross-platform game engine and development platform created by Unity Technologies. With Unity game developers can build high-quality 3D and 2D games, deploy them across mobile, desktop, consoles, VR/AR or the Web. Unity was first released as OS X-exclusive game engine but as of 2018 the engine had been extended to support more than 25 platforms.

Torque 3D is a premier open-source game engine. Torque 3D includes both a high-performance forward-rendering basic lighting engine, and a deferred-rendering advanced lighting mode. A plugin system for physics, and networking capabilities with a server authoritative networking model, used for multiplayer games. The game engine has been used to create everything from driving simulators to MMOs to first-person shooters.

Amazon Lumberyard is a free, cross-platform game engine based on the famous CryEngine. With Amazon Lumberyard, you can create games without royalties, seat fees and additional costs. Since the game engine is developed by Amazon it provides some interesting integrations out-of-the-box. Lumberyard provides frictionless integration with Twitch and AWS for hosting and displaying and promoting your new game.