Microsoft was '81 for acquiring DOS (and that's technically a lie, they didn't have the source code for several years later. but it's how they convinced IBM)

both MS and Apple were living BASIC at this time. Basic is not a operating system, it's a pre-compiler environment. it's designed to let you run code directly without machine code. as assembler and C was not a thing or rather licensed yet.

BSD specifically Netbsd exists as they were part of the invention of C code. BSD was ported from assembler/machine code to be portable with C.

MSdos, which Microsoft acquired by buying Qdos (aka 86dos), was written by a developer who stole most of the code and copied the rest from a existing operating system (which I cannot recall at this time). both were In negotiations with IBM. just Microsoft lied through their teeth to get the contract and won.

apple at the same time had fallen behind. the Lisa and apple II were still running a basic interpreter on top of ROMMON. Wozniak who wrote ROMMON and later large portions of apples next two OSes including OSx. kept pushing to get a actual Unix like Operating system on the device.

however Steve jobs was cruel, and demanded no new changes... it's why Wolfenstein was nearly out before a true OS existed from Apple... Steve had a long history of trying to control advancement through forcing model version advancements with weaker hardware than the previous so you would be encouraged to upgrade.