Showcase: Beyond Protocol.
If you are looking for a complex space strategy game, there used to be a great game called Beyond Protocol. It was a persistent universe MMORTS which allowed you to build a huge planet and space empire, featuring very complex design. You could design planetary buildings, units, naval ships, space ships and space stations. You could customize these extensively: weapons, radar, armour, engine etc. You could build colonies much like you build bases in Starcraft, with many different buildings. You could mine 100+ different minerals and use them for designing armour, weapons etc. But you could also go to space and build space stations and custom-designed combat ships from small fighters to massive battleships. And move to different planets and even different star systems to build more colonies. You could have massive PvP battles with hundreds of units attacking each other in space and on planets.
short videos showing a large battle in space:
https://www. youtube. com/watch?v=gPGyOxKf010
https://www. youtube. com/watch?v=if6kWjoOeSk
It would have been the perfect niche game except the devs royally messed up game balance. The learning curve for newbies was too steep, and when the game came out, a handful of aggressive veterans from beta destroyed all the newbies, chasing most of them out of the game. Technically, the game worked great and it looked great. But it was a commercial failure and after a few years the servers were shut down.
The source code was put on Sourceforge and one of the players, SirParadox, revived the game under the name After Protocol, making it available for free for whomever wants to play. It is mostly peaceful nowadays since there are not that many active players.
Download the game client on www. afterprotocol. com
more info and screenshots on
https://www. beyondprotocol. org/
Tutorial series:
https://www. youtube. com/watch?v=Mjjs1tnbjn8&list=PLm10QcO_qhG1tt5UKj6jon9JrAKGtHTSC&index=2
More game videos:
https://www. youtube. com/watch?v=OGZwfCq1hE4
https://www. youtube. com/watch?v=fp-3NxicLCg