TripleA - TripleA is a free (under GPL) turn based strategy game based on Axis & Allies board game.
Unity - The multiplatform game creation tools for everyone.
Lux Delux - Lux Delux is a game of strategy and domination inspired by the board game Risk.
Godot Engine - Feature-packed 2D and 3D open source game engine.
Streets of Chaos - Streets of Chaos is a Puzzle, Tactical, Turn-based Strategy and Single-player Simulation created by SimProse Studios.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.