Is Macintosh System Software 1.0 (Classic MacOS) Free?
No, System 1.0 is not open source and not in the public domain. Apple provided it with the purchase of a Macintosh. The system software was not available for separate purchase.

History

With MacOS 1.0 you are probably referring to the first version of Apple's operating system. 

In 1984, with the release of the first Macintosh (128K), the system was actually not called MacOS but was just Mac System Software.

Apple has called it MacOS since version 7.6. 

You can read (and learn) a lot about it on Wikipedia. 

Emulation

About an emulator of the first Mac system. There is one you can use : mini vMac


It will require a ROM to run vMac
and finally a disk image of the system


Unzip everything, start the mini vMac, it will load the ROM and you'll get a blinking floppy with a question mark because it couldn't find the system. To solve it just drag the system image over vMac and the system will start !