| Compliance with various POSIX standards remains useful and relevant, though the only list of actually certified products I can find[1] includes only RTOSes. Even without certification, POSIX remains a useful baseline for implementing and consuming cross-platform system services, taken with your suggested grains of salt on the consumer side for any details not specifically documented as POSIX-compliant. UNIX certification seems mostly only relevant in terms of OS marketing, in the sense that it signifies a vendor's intention to provide a usable POSIX-ish programming environment. As a target for cross-platform application developers, the list of certified UNIX platforms is at best weirdly specific: macOS: supported AIX: supported, though even IBM seems to prefer Linux for new development; IBM-supported Linux runs natively alongside AIX on the same hardware, further limiting appeal z/OS: supported, but only a "UNIX system" in that it offers a POSIX compatibility layer on top of a system that's fundamentally non-POSIX in design (EBCDIC, expensive process creation, etc.); IBM-supported Linux runs natively alongside z/OS on the same hardware, further limiting appeal HP-UX: supported until 2025-12-31; Itanium-only SCO UnixWare and OpenServer: supported (?), but no substantial updates since 2018 (?) [1] https://posix.opengroup.org/register.html |