Unity - The multiplatform game creation tools for everyone.
TurboSquid - TurboSquid offers 3D models for professionals.
Godot Engine - Feature-packed 2D and 3D open source game engine.
3DOcean - 3D Models & Accessories From $1 for 3D Models, Textures, Materials & Shaders, 2D Concepts...
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
STLFinder - The 3d models search engine.