> It makes sense to have one stanfard across the world. This way good software can come from multiple countries.

TRON was not the only attempt to define a standardised operating system API in the 1980s. As well as TRON and POSIX, another was IEEE Std 855-1990 (Microprocessor Operating System Interface or MOSI for short). But POSIX was the only one which really succeeded.

MOSI is pretty obscure, but my impression of what happened there – in the early 1980s, 8-bit platforms were widely popular, but very incompatible with each other (e.g. software written for Apple II could not run on Commodore 64 even though they both had 6502 CPUs). So the proposal for a common OS API was made, and an IEEE standards committee started standardising it. But by the time the standard was finished, those 8-bit platforms were declining, and IEEE was left with a standard focused on the needs of a declining market, and so very few ever used it. [0] (MOSI itself isn't inherently 8-bit – like POSIX it is a source-level standard rather than a binary-level standard, so could be used on 16-bit or 32-bit systems – but its feature set was a lowest common denominator of what 8-bit systems supported, so not very attractive for machines that have the memory to do much more.)

In 1988, the Japanese education ministry decided to make BTRON the standard operating system for Japanese schools. From what I understand, this move frightened Microsoft (among others), who feared that it would prevent DOS/Windows from being used in Japanese schools, or else force Microsoft to add a BTRON compatibility subsystem to their operating systems. So Microsoft lobbied the US government to pressure the Japanese government, and that pressure resulted in the Japanese education ministry dropping the requirement for BTRON, which in turn largely killed BTRON off. It didn't completely die; a variant of BTRON (Cho-Kanji) continues to be developed into this century, but it is a niche product whose primary value proposition is far more comprehensive support for obscure Kanji characters than mainstream Unicode-based operating systems (maybe useful if you do research into historical Japanese texts). Another factor in killing the Japanese education ministry's requirement for BTRON, was domestic opposition from NEC – at the time, NEC PC-98 machines running DOS were the de facto standard in the Japanese education system, and BTRON threatened NEC's dominance of that market. It could well have been a combination of both external pressure from the US government and internal pressure from NEC that killed it.

Related is Ada Programming Support Environment (APSE) and Common APSE Interface Set (CAIS). Part of the US DOD project which resulted in Ada, whose requirements demanded not only a standard programming language, but also a standard development environment, with APIs for integrating with compilers, editors, version control, build tools, etc. CAIS is standardised in MIL STD-1838A. So it is like POSIX/MOSI/BTRON, a cross-operating system API, albeit one focused on the needs of software development rather than general purpose computing–implementations of CAIS existed for Unix, OpenVMS and MVS, so development tools written against the CAIS API could run on all three operating systems. And the US government poured untold amounts of money into it, but I'm not sure if anyone ever used it. Probably some military projects did.

And APSE/CAIS in turn inspired PCTE (Portable Common Tool Environment), which was basically the EU's answer to APSE/CAIS. And just like APSE/CAIS, it consumed large quantities of EU research funding, before eventually being forgotten without ever seeing much if any real world use. It is standardised as ISO/IEC 13719–which apparently nobody uses, but ISO keeps on renewing because withdrawing a standard consumes bureaucratic resources, and PCTE is so obscure nobody even wants to expend the effort on withdrawing it.

[0] There was an implementation of MOSI for CP/M-80 and Pascal-MT+ – you can find it at https://github.com/skissane/MOSI/ – but I doubt that ever saw much use.