LDraw - LDraw is an open standard for LEGO CAD programs that allow the user to create virtual LEGO models...
Unity - The multiplatform game creation tools for everyone.
LeoCAD - LeoCAD is a CAD program for creating virtual LEGO models.
Godot Engine - Feature-packed 2D and 3D open source game engine.
BlockCAD - BlockCAD is freeware software for forming virtual models with Lego-like bricks.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.