Hi, there are several operating systems in use today, they vary by multiple facets including device, function, use cases etc. Generally, there are multiple versions of a particular operating system in use.
For Personal Computers, the most prevalent operating systems are Microsoft Windows, Linux and MacOSX. For Servers running in data centers, there are myriad operating systems, many Unix-based, Linux, and Windows flavors are around. For Mobile devices including smart phones and tablets, Android, IOS and others are prevalent today.
Other operating systems have come and gone.
You can find good information on Operating Systems in general and even on specific operating systems on the web. Wikipedia is a good place to start.
This article goes over operating systems and some history: https://en.wikipedia.org/wiki/Operating_system
I hope this helps.