GalCiv was the first PC game for OS/2
Here's a blast from the past: https://www.stardock.com/products/gcgold/"Galactic Civilizations was OS/2's first original commercial game designed from the ground up to take advantage of all of OS/2's powerful features."
It's pretty hard to find OS/2 info now, since they quit developing it years ago.
WindowBlinds was the first windows retail program..? The first Windows product for Stardock, yes.