Overview
MacOS is a feature-packed professional operating system written by Apple. It is based off FreeBSD, and uses Apple's UNX kernel, which is based on Unix. MacOS is free for everyone, although technically only licensed to run on Macintosh computers (made by Apple).
Pros and Cons
Pros:
Made for Productivity
MacOS ships with Pages, Keynote, and Numbers, Apple's free productivity suite. Microsoft Office is also fully supported on MacOS, as well as a host of other professional media applications.
Simple, clean User Interface
MacOS's user interface is very clean and simple when compared to other operating systems, especially Windows 10.
Enhanced system security
MacOS is less likely to become infected with malware. Apple is on top of security and releases security updates regularly. MacOS also comes with FileVault, a full-disk encryption tool that decrypts the drive on boot and re-encrypts it when shutdown. This means that someone stealing a Mac with FileVault enabled will not have much luck getting into the owner's files.
Compatible with other Apple systems and devices
You can sync your Mac seamlessly with iOS devices and other Macs via AirDrop, iCloud, etc.
Software is well-fitted to the hardware
Apple uses high quality hardware for Mac computers, resulting in less freezing and smooth performance. MacOS apps are designed specifically for the Macintosh hardware.
Super easy multitasking
MacOS provides several different methods of multitasking, including Mission Control and dynamic desktops.
Cons:
Restricted Application Availability
MacOS applications are not as common as Windows applications, simply because Windows is more mainstream in general. Not as many developers write apps for MacOS, although there is a huge selection of Apps that are written for MacOS.
MacOS is not for Gaming
MacOS is geared more toward developers and professionals than gamers. This is because of the lack of super powerful graphics in Macintosh computers. Most modern video games require extensive GPU power, and most Mac computers (that are not the new Mac Pro or that are not paired with an external GPU) simply don't have the graphics power for gaming.
Popularity
StatCounter estimates that MacOS runs on 9.4% of all personal computers. While MacOS is not as popular as Windows, a good amount of people still use and rely on it.