TripleA - TripleA is a free (under GPL) turn based strategy game based on Axis & Allies board game.
The Battle for Wesnoth - The Battle for Wesnoth is a turn-based tactical strategy game with a high fantasy theme.
Domination - Domination is a game that is a bit like the well known board game of Risk.
FreeCiv - Freeciv is an open-source, turn-based strategy game based on Civilization II.
Ticket to Ride - Ticket to Ride is a Turn-based Strategy, Puzzle, Board, Co-op, Single, and Multiplayer video game created and published by Days of Wonder and Asmodee Digital.
Sid Meier’s Civilization VI - Sid Meier’s Civilization VI is a Turn-based Strategy, War, Tactical, Single and Multiplayer video game created by Firaxis and published by 2K.