We actually rely upon two different operating environments for COBOL that do not originate from IBM.

The first is OS2200. Our final major application on this platform was complete by 1970, and links COBOL into assembler that accesses the hierarchical DMS database. The first SMP port of UNIX was to this hardware:

https://en.m.wikipedia.org/wiki/OS_2200

The second is VMS, specifically the VAX variety. VMS bundled a COBOL compiler, which we used to write ACMS applications.

https://en.m.wikipedia.org/wiki/OpenVMS

We continue to produce new COBOL code for both.