I'm as Linux Systems Administrator by trade and have been running GNU/Linux since 1998 as my sole Operating System (OS) and earn my keep that way too.
I like what I do and can't not stop doing it so I have a homelab to install, run and test things + use it for development etc. Aka it is my playgrounc.
Well it can be many a things. For me it is 4 small machines that I use to run things on.
I've chosen to use a hypervisor on 3 of the servers and use the 4th as storage/backup.
The hypervisor I've chosen is Proxmox. I've tried XCP-ng for a few years and I like it as it resembles my work but over time you like to play around so I'm running Proxmox now.
Proxmox is a type-2 hypervisor that is used to run Virtual Machines (or containers using LXC). Type-2 means it runs a OS and then uses a separate application to do the irtualization - in Proxmox'es case it is KVM which is part of the Linux kernel that the OS runs - which is Debian.
A Virtual Machine or VM is just that a machine that runs with virtual hardware on another maching. The virtualized hardware can with the help of KVM or Xen or ESXi etc. it can actually be allocated real hardware that is shared by the hypervisor. So all in all a VM is just like any other machine but with virtualized hardware that is usually actually actual hardware the hypervisor shares with the VM or VMs running on the hypervisor.
This physical hardware access is possible because a machine (the CPU that actaully does the work) is idle most of the time and the hypervisor will allocate hardware when it is actually needed. It does sometimes introduce some reduced "hardware" for the VM that can usually be 1-10% of the actual hardware if the VMs are all using a lot of CPU at the same time.
Memory can be balloned aka it is usually directly mapped to hardware memory but since it is virtualized it can be "zeroed" out when not in use and/or swapped to hardware meaning even though the VM has 10GB of RAM then it might actually only have 4GB alloated no hardware and 6GB is "just" accessible via registers like normal but not actually allocated or it is swapped to disk by the hypervisor without the VM actually knowing.
Well as I started stating then I'm a sysadmin by trade and heart as I've been more interrested in getting my first PC (a 80286 back in the day (yes I'm old)) running optimally and use its resources as best it could and in 1998 I got into GNU/Linux and I've not looked back since (well I did install Windows on a spare m.2 SSD during Covid lockdown to play CS and CS2 but I've stopped playing that since ~late '24).
So all in all I like to mingle and get things working.
That is a good question.
For one I like to run things I use at work and things I have an interrest in.
Some of the work things I won't mention here as it is not my place to tell, but some of my mentions might be enterprise tools and others are just my things I'm tingering with.