Caesar 3!

OpenRA is an open-source reimplementation of Westwood’s Command & Conquer: Red Alert game engine, updated to use the hardware acceleration of modern video cards using OpenGL.

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.

CaesarIA is an open source remake of Caesar III game released by Impressions Games in 1998, it aims to expand the possibilities of the classical city-building simulators and to add new features showing the city life. Now the game work with Windows, Linux, Mac, Haiku and Android.

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. »

Globulation 2 is an innovative Real-Time Strategy (RTS) game which reduces micro-management by automatically assigning tasks to units.

[Link from Wayback Machine: http://web.archive.org/web/20010330133302/http://www.pharaoh1.com/main_index.shtml ]

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! »