CaesarIA!

0 A.D. is a free, open-source, cross-platform real-time strategy (RTS) game of ancient warfare. In short, it is a historically-based war/economy game that allows players to relive or rewrite the history of Western civilizations, focusing on the years between 500 B.C. and 500 A.D. The project is highly ambitious, involving state-of-the-art 3D graphics, detailed artwork, sound, and a flexible and powerful custom-built game engine.

Set a generation before the events of the original Warcraft began, Warcraft II is a real-time strategy game by Blizzard Entertainment. Cunning, sinister, and seemingly unstoppable, the demonic Burning Legion prepare to launch their long-awaited assault on the mortal world. Survival is a matter of strategy, as the Reign of Chaos begins…

MegaGlest is an open source 3D-real-time strategy game, where you control the armies of one of seven different factions: Tech, Magic, Egyptians, Indians, Norsemen Persian or Romans. The game is setup in one of 14 naturally looking settings, which -like the unit models- are crafted with great appreciation for detail.

Age of Mythology is based on building towns, gathering resources, creating armies, and ultimately destroying enemy units and buildings. In this way, players are able to defeat and conquer rival towns and civilizations. Players advance their tribe through four "Ages": starting in the Archaic Age, the player may upgrade to the Classical Age, the Heroic Age, and finally, the Mythic Age. Each upgrade to a higher Age unlocks new units and technologies for the player, which strengthens their settlement. »

Free (as in freedom) open-source RTS http://alternativeto.net/software/age-of-empires-iii/ engine. Written from scratch in C++14 and Python, using OpenGL + GLSL.

Dune Legacy is an effort by a handful of developers to revitalize the first-ever real-time strategy game. The original game was the basis for the hugely successful Command and Conquer series, and the gameplay has been replicated an extended to a wide variety of storylines and series. Lead one of three interplanetary houses, Atreides, Harkonnen or Ordos, in an attempt to harvest the largest amount of spice from the sand dunes. Exchange your spice stockpiles for credits through refinement and build an army capable of thwarting attempts of the other houses to stop your harvesting! »