Cocos simplifies game creation and distribution with Cocos Creator
Open source cross-platform multi-purpose game toolkit
scene-oriented, flexible 3D engine (C++, Python, C#, Java)
Multi-platform Engine for Desktop, XBOX (UWP) and Mobile games
Open source library for creative expression on the web, desktop, etc.
GLScene Engine for Delphi & C++Builder VCL Windows 32/64
... the open-source glide computer
GEDKeeper - opensource and crossplatform genealogy management program
The Atomic Game Engine is a multi-platform 2D and 3D engine
Open-source, cross-platform, C++ game engine for creating 2D/3D games
3D .NET engine for Windows, Linux, Mac
Dragging and Dropping Components for Multi-projection Applications
Egret is a brand new open mobile game and application engine
PixelLight is a cross-platform application framework