Who were the creators of these retro systems?

[SoftPCMuseum]

MS-DOS: Bill Gates had very little impact on the design only working on a couple of the demonstration BASIC games. Bill Gates wrote the checks to SCP to pick up QDOS and cashed from IBM and others. Tim Paterson was responsible for creating the 8086 OS inspired heavily by CP/M with file system derived from MS Disk Basic. A host of other people modified and fixed QDOS as it turned into the PC/MS-DOS everyone knows.

MAC: look at folklore.org to see how many people were responsible

That is the problem with a lot of popular history. Often credit is assigned only to the person who was CEO while the work was done by dozens of people.

Most of these systems have webpages that explain the development and list the major people.

Quite correct; DOS originally started out as a project by Tim Paterson.

Originally, in late-1979, SCP (Seattle Computer Products) released an S-100 board machine with an Intel 8086 CPU. However, there was no operating system for it, whereas other (mostly 8-bit) machines of the time ran operating systems such as CP/M.

It was for this reason that in April that year, Tim Paterson started work on a new operating system for the machine, known as "QDOS" (Quick and Dirty Operating System), which was similar to CP/M in certain areas but which differed in others. It was basically designed to provide a CP/M-like environment for the 16-bit Intel 8086 CPU, and was eventually renamed to 86-DOS (8086 Disk Operating System).

In about 1980-1981, Microsoft was one of the licensees of 86-DOS, along with several other companies from what I remember. They were also providing the software to IBM for their "Project Chess" computer, which SCP found out about several months later.

Tim Paterson was employed at Microsoft in May 1981 to port the software over to the new IBM Personal Computer, and the boot sector for the very first version of The IBM Personal Computer DOS 1.00 dates back to around that time if I remember correctly.

Technically speaking, programs written for 86-DOS can still run on MS-DOS, including the earlier versions of the command line utilities which were provided with 86-DOS. 86-DOS also brought over the .COM program format from CP/M while CP/M-86 did not, and many of the early MS-DOS programs were direct ports of their respective CP/M versions (WordStar for example).

 

[FishFinger]

Bil Herd was the lead designer of the Commodore 128. He occasionally posts a few stories about the time on Youtube.

 

[Scali]

Atari designed the Commodore Amiga.
No really Well, (former) Atari employees anyway, most notably Jay Miner (he also did most of the Atari 400/800 btw).