There was ISODE (https://en.wikipedia.org/wiki/ISO_Development_Environment).
I recall experimenting with it but didn't actually use it in anger.
Ditto.
I know that DEC/Compaq/HP Tru64 Unix (nee OSF/1) came with a OSI stack -
we had customers who wanted/used FTAM and I was surprised to find it
came with the OS.
Tru64 talked to DECnet Phase X (I don't remember which one, maybe 4 or 5), which had become an ISO/OSI stack by that point for political reasons inside of Digital (the OSI vs TCP war reminded me of the Pascal vs C and VMS vs UNIX wars - all very silly in retrospect, but I guess it was really about who got which $s for development).
Clem