Unity - The multiplatform game creation tools for everyone.
Invision - Prototyping and collaboration for design teams
Godot Engine - Feature-packed 2D and 3D open source game engine.
Proto.io - Create fully-interactive high-fidelity prototypes in minutes that look and work exactly like your app should. Sign up for a free 15-day trial and get started.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.