OpenTTD - An open-source clone of the classic game ...
Unity - The multiplatform game creation tools for everyone.
SimCity BuildIt - Build, craft, and control! SimCity BuildIt is an all-new SimCity game designed just for mobile.
Godot Engine - Feature-packed 2D and 3D open source game engine.
Cities: Skylines - Cities: Skylines is a Construction and Management, City Building, and Single-player Simulation developed by Colossal Order and published by Paradox Interactive.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.