Mega-lo-Mania, an RTS that I never ever see discussed outside of, occasionally, in the Amiga and Mega Drive circles.
It hasn't aged fantastically, but I feel like the core concept could be expanded into a much fuller game. I still sometimes play through it completely in one sitting, though.
Really quickly makes you hate Nukes, though.
This came out in the US as "Tyrants", and likewise I still think about it occasionally.
It is frustrating how your starting position can make you lose based on the resources you get (and the computer players pick their positions so quickly you often have few options). It's a fun game, though, and I like the "epoch" system where you prioritize how many of your people to use on each island.
If it were a little slower paced (I know, ironic in a game where you can determine the game speed) in that you have time to react to invasions, I'd have more fun with it. It was pretty rare that I got to the point where nukes were even an option.
Though I'll avoid posting pictures, I miss some of the weird Koei simulation games from the late NES/early SNES and Genesis era.
Aerobiz Supersonic has already been mentioned, but they also created:
Gemfire, a weird fantasy take on a pseudo-English civil war that got a Japan-only sequel
Liberty or Death, an entirely too complicated lopsided American Revolution strategy game,
Uncharted Waters (and its sequel), an Age of Discovery open strategy/exploration game
Genghis Khan II, a late middle ages strategy game that had no business having weird heir-raising mechanics and the more I read about what was cut out from the romance system the weirder it is
Inindo, a Sengoku-era ninja JRPG with ongoing strategy "minigame" constantly running in the background (you can offer your services to various lords who are fighting Nobunaga and participate in wars, also there are other "free agents" running around that can join you or will challenge you to duels)
I'm pretty sure there are a few more I'm not even thinking of. I think P.T.O. was theirs too and it seemed even more complicated than most of these.
They made a ton of weird, mechanically deep games and I'm surprised they are somehow still afloat after all that (yes, I know the answer is probably Dynasty Warriors and the Tecmo merger).