Check out Asset Forge, a toolkit that allows anyone to create 3D models and 2D sprites using building blocks. Finished assets are said to be compatible with most available game engines.
How it works
What you gain is an access to a large library of pre-made blocks, they’re each grouped in different categories. You can place an unlimited number of blocks in your creation after which it’s possible to export and use in the game engine for your choice.
- Move, rotate and flip blocks
- Apply colors and textures
- Export as OBJ or FBX file formats
- Render your model as PNG
The exported models are compatible with most game engines including Unity, Unreal, CryEngine, Blender and ThreeJS. The 2D sprites (PNG) are compatible with all game engines.
You can find more detail on the tool and FAQ here.