I can add Homeworld and Supreme Commander (1, 2 is pretty bad imo) for real time, my top two choices of all time, and Alpha Centauri for turn based.

All three as as close to perfection as you can get, imo.

Sorry for the necro, but saw this thread linked in the SRPG thread and thought it would be an appropriate place to ask.

Anyone played 0 AD? I only vaguely recall hearing about it some ten or so years ago and have not really heard much about it since then. Mostly curious if it plays similar to any other RTS out there.

I played, modded, and briefly considered a total overhaul of, 0AD. Its doing well. Has some major differences from many RPGs. It isn't quite to the point it wants to be. Formation/battalion gameplay isn't finalized for instance. However the art assets are amazing and there are some great mods. Go to the Wildfiregame forums for more info.

This is by far the best open source strategy game, and probably one of the best historical-themed RTS.
About its gameplay, it is really similar to the Age of Empires games.

Star Trek Armada 1 & 2. Both just released here on GOG. Great Games

Total War Warhammer 2. Soon to be Total War Warhammer 3.

I'm not a big fan of strategy games, I like more to turn off my brain after a long day of work and play something more simple like a shooter. Yet I think this recommendations maybe interesting for you, coming from somebody that don't liie strategy game the games must be really good to actually like me.
1- Heroes of Might and Magic 3 and 5, both games are obligatory. Well balanced and super fun, you woll lose track of time and will forget to feed your hamster... Or your child, make sure to be the first one and not the last.
2- Original War, pick up this one quite recently on the sale because I saw the recommendation on a thread, and was a great surprise, as good aa they said and even more, intereating story and fun gameplay.
3- Shadow Tactics Blade of the Shogun, is like Commandos but newer, and everybody loves Commando, if you hates Commando you are wrong or crazy, you can't say Commando enough... Also, Commando is recommended too.

id suggest warcraft 2, warcraft 3, or masters of orion. warcraft 3 was easiest to get into but all are fun. Also not sure if the game called Z counts but its fun n easy.

Those 2 are definitely the highlights of the series, but balanced and HoM&M 3 simply can't be in the same sentence. Once you start going below the surface level, you will realize that the game is so horribly imbalanced on so many levels, it's not even funny. Skills (a big chunk of them being basically useless), spells (berserking 3/4s of the enemy army once battle starts or Earth Magic having the best in class spell for pretty much everything), towns (Conflux is beyond broken), hero specializazions, you name it.

XCOM: Enemy Unknown Complete Pack and Xenonauts
Both are great games that force you to be competent both on the battlefield as well as in managing your own base. Being lacking in either of those will definitely make the games harder, more so when you don't spend as much time researching whatever it is your troops have salvaged on the battlefield (and ofc, equipping your troops with the new technology your engineers have created by borrowing the ideas from the aliens).

World in Conflict: Complete Edition
This game has a great story that makes you feel attached to the characters you play with throughout the campaign. With that aside, the game's mechanics are solid, especially the way the game developers did justice to how they implemented the support role in the game (tactical strikes, etc.).

Field of Glory II
If you're waiting for any of the Total War games to ever come on GOG, you might as well settle with this game. The only downside is of course, this game is a turn-based strategy game (that is if you prefer real-time strategy games, which is why I mentioned about Total War first). That said, the game does offer many features that you will find to be both realistic and logical, especially for games that revolve around ancient battles. To know more about what I'm talking about, you can simply look up on the internet some threads where users would pin Field of Glory II and Total War games against each other to determine which among them is the better game. P.S.: The AI in this game is smart.

Homeworld
Similar to World in Conflict: Complete Edition, I really like the story of this game. That said, I was and still am not really that good at this game lol. Why? I guess it's because the game can be super intense sometimes. Also, if you're planning on getting this game, know that you shouldn't be too greedy and flood your battalion with as many ships as possible in the campaign, because if I remember correctly (please correct me if I'm wrong), in the final mission, the number of the enemy's units will be adjusted to how many friendly ships you have at your disposal. Therefore, if you happen to have too many, be prepared for the worst.

Sid Meier's Civilization IV®: The Complete Edition
This game has perhaps consumed the most game time for me compared to all the strategy games that I've listed above. In short, one, more, turn...

Honorable mention:
BATTLETECH
I really want to like this game, but the game is really badly optimized. And it seems to me that the game is much better modded, because through modding, also comes with it more mechs that you can choose from as well as a bigger galaxy map (knowing Paradox, you need to pay for the game's DLCs to gain access to the additional mechs and maps that the game has to offer). Lastly, for me, the arts of the game are pretty.

All the games I've mentioned can be found here on GOG.

strategy game you said, here you get the best one ever to existed.

https://www.youtube.com/watch?v=FP6zxwCCCDc

Honestly, I don't see anything "honorable" about it. Cliche story, bad optimization, multiplayer/skirmish has only one mode (no wonder very few people play it).

I think you will be better with MechCommander that is considered abandonware today and thus can be downloaded for free from such sites as MechCommander.org.

Honestly, the reason why I even mentioned it in my post was simply because I did enjoy the gameplay quite a bit. But, like you said, I eventually got sick of the bad optimization, especially the memory leaks, of the game.

As for MechCommander, I've never tried the game but have actually seen some gameplays of it. Do you know Brigador: Up-Armored Edition? I think you might enjoy the game if you like MechCommander.

Mech warriors is and always will be niche marketshare.
it's sad because i really like MWs lore.