Hah, that's a funny story. OS/2 was in good part developed by Microsoft and in 1.x it shared plenty of APIS. IBM took over when they realized Microsoft is preparing for a coup capitalizing on the success of Windows 3.x, but it was too late. Microsoft cut OS/2 at the legs by leaving it on Windows 3.x (cutting it off from the upgrade paths), they controlled the ecosystem (OS/2 is windows compatible, right ?) and what MS originally developed as OS/2 3.0 became known to the world as... Microsoft Windows NT (the first versions of NT even supported OS/2 filesystems and vestigial APIs). Realizing they are being ****d big time, IBM did a last-ditch effort with their own OS/2 3.0 Warp, even tried to combat the lack of native apps by embracing Java (getting on-topic, woo !). Now, with the performance of Java at the day, this did not help the slightest bit (I pity everyone who tried JavaOffice on a 386), and the lack of apps, drivers, and MS striking deals for having MSDOS/Windows being sold in bundles meant a nasty death-spiral for OS/2.

It was many summers ago, but that is how I remember that story.

OS/2 tried to gain traction from an existing ecosystem through compatibility not once, but twice, and both times failed horribly, exactly because of lack of native 'killer application' momentum.