Best free "real-time strategy" games

GAME GENRE - A real-time strategy game, often abbreviated as "RTS", is a type of video game where players control and manage various units and resources in a dynamic, real-time environment. These games emphasize strategic planning, decision-making, and multitasking. In an RTS game, players typically have control over armies, civilizations, or factions and are tasked with defeating opponents through military, economic, and often diplomatic means.
Popular examples of real-time strategy games include "StarCraft", "Age of Empires", "Command & Conquer", "Warcraft", and "Total War" series. These games vary in terms of settings, objectives, and complexity, but they all share the common real-time strategy gameplay elements.