IBM has built several operating systems and programming languages and compilers over the years. Probably more than Bell Labs, actually. It's not so surprising.
Unix and C is more known, so that would be my assumption too. In fact I can't name any IBM made OSes or programming languages.
Aix and z/os are popular operating systems by ibmsl still in use, not counting things like system/36. Lime is a research pl at I'm, there is also apl which was made at Harvard and later at ibm.
FORTRAN. A pretty important one.
I can name a half dozen without googling. But, I'm kinda old and I remember when IBM was the dominant force in computing at nearly all levels.