It’s an operating system itself but it’s only job is to allow you to run virtual machines.
It has a web gui allowing you to vnc* and interact with the virtual machines using only your browser, or you can install apps on your PC for a better experience.
You can limit the resources that each VM has, only a portion of the RAM, only some of the CPU threads etc.
It has a free version, but IIRC the free version limits you to 8 CPU threads per VM.
You can also pass through hardware to an individual VM, .e.g. a whole graphics card and a USB keyboard/mouse. This means that if you were looking at the monitor and using the keyboard/mouse then you wouldn’t be able to tell it’s a VM. If you had two of each peripheral, you could run two local machines from a single tower.
I think Linus did something similar with unraid (same idea) and ran 8 (?) gaming VMs from a single tower using 8 GPUs, 8 monitors etc.
Note that nvidia doesn’t like you using GPUs in VMs and actively fights against it in the drivers but there are workarounds.
