One action a turn: tap a ? to explore, a green-edged tile to found a city (8 gold), a city to grow it (3 gold + 2 per level). Each city pays 1 + its level every turn.
Your capital (C1) sits in the fog. Twenty turns: earn as much gold as you can.
A 20-turn 4X economy toy. Our own simplified model, not taken from any game.