An OS is system software - it manages computer hardware, and software resources/application programs, and provides common services for computer programs. For hardware functions - like input & output (IO) and memory, the OS acts as an intermediary between programs and the computer hardware.
Operationg Systems - PC's/Desktop
Microsoft Windows is doninating the market. This is the de facto standard for home and business.
macOS by Apple
Apple is in second place to personal computers. Macintosh line of PC's and workstations.
Linux is in third place to personal computers. To provide users a free alternative. It is efficient and a fast performaing system.
Operationg Systems - Mobile Devices (Smartphones & Tablets)
Android by Google
Google's Android dominate the market of smartphones.
iOS by Apple
Apple is in second place to the smartphone market.
Operationg Systems - Server & Supercomputers
Linux distributors dominate the server and supercomputing sectors.
Operationg Systems - Embedded (ATM's, airplane systems, IoT devices...)
Embedded Linux is a good example of embedded OS. The OS is normally strippeddown and dedicated to specific performance.
Real Time Operationg Systems - RTOS (ie. power plant control...)