Desktop/Android/HTML5/iOS Java game development framework
2D GPU-accelerated framework for ActionScript developers
Kotlin Multiplatform bindings to Skia
Orx: Portable Game Engine
Delphi : VRCalc++ OOSL & + (Paged List, TextEditor, VRAstroVision ...)
Everything you need to build and deploy scalable realtime 3D apps
ZED OS the clone of Windows XP
Cocos2d for iOS and OS X, built using Objective-C
The Perfect core toolset and framework for Swift Developers