VMware Workstation is an application that allows to install multiple operating systems on the same computer. For example, if you install VMware Workstation on a Windows computer, you can install many other operating systems such as Mac, other Windows versions, Linux etc. and use your computer running on ay desired OS.
It does not requires restart and users can easily start another operating system any time. Using another operating system on the same machine will have all benefits like using a separate computer, you can use internet, install applications for that OS and so on.
Good to test different applications on different operating system using a single computer, good to install and use applications that works only on specific operating systems, even you have only a Windows or Linux.
This application basically reduces your hardware costs; instead buying new computer to have different operating systems, use a single one and VMware will allow to install many others.
Can share files between virtual computers, supports drag&drop, forward keyboard if you need, save snapshots (backups), protect access with password and others.
Is recommended to have good hardware capabilities (processor, RAM memory and HDD space) because each new installed OS will need some resources to run properly.