There are numerous Operating Systems available. Most commonly used Operating systems are Microsoft Windows, macOS and Linux.
Linux Mint
Beginners would find it extremely easy to use. While power users can utilize it to the limit.
Fedora
It is known for integrating latest tech. So, users get to try new features as when they are available.
Ubuntu
Its a feature rich OS. Apart from the Desktop version we have got 8 different Ubuntu flavors.
openSUSE
A highly polished Operating System. It utilizes openQA, an automated test utility, for Quality Assurance.
Elementary OS
For its beautifully designed Desktop Environment, Pantheon.
Most Linux-based Operating systems are Free and open-source.
Linux-based distributions are also utilized in High Performance Computing (HPC) environments as well.