I worked for an IBM subsidiary in the early 90s while they were building and releasing HPTS. Our sub did ancillary products for HPTS and 3890 sorters, all in “c”, assembler, and running on OS/2. The OS/2 API was, IMO, more logically designed and documented than anything since. It was a blast. Sadly, OS/2 didn’t survived. But, it was fun while it lasted.