OpenSourceGames

From website:

A classic, turn-based strategy game with up to four armies fighting against each other. Challenge yourself in a campaign against AI, or a hot-seat battle with a friend. Using the easy map editor you can create any imaginable scenario to play!

ToF II follows in the footsteps of the original Tanks of Freedom and brings even more fun and depth. Take command of new types of units, use their powerful abilities, and turn tides of battles with many unique heroes. Experience new stories in four dedicated campaigns, or play skirmishes on a new set of maps!

This game is an open-source hobby project. All assets and code can be found on the Github page.