Open-source engine for Heroes of Might and Magic III
Powerful, mature open-source cross-platform game engine for Python
3D Procedural Game Engine Using OpenGL
Voxel game-creation platform with easy modding and game creation
KorGE Game Engine. Multiplatform Kotlin Game Engine & Korlibs
Free, open source game engine online
Multi-threaded game engine for Android
Little game background framework in java.