Proxmox VE is a Linux distro based on Debian 11 to manage and run virtual machines.
It was originally used only for servers, but I see now more and more videos popping up on YouTube where Proxmox VE is used in regular desktop environments.
It has many unique features you won't find in virtualization solutions such as VMware or VirtualBox. For example, you can add your real hardware, such as graphics cards, to your virtual machines. This means fully accelerated graphics performance like on your regular PC but in a virtual machine with very little overhead.
Other unique things include a TPM 2.0 emulator to run unpatched Windows 11 on unsupported hardware. An emulator for the Apple SMC chip to run unpatched macOS etc.
MultiBootUSB is a software installer that allows the user to install multiple Live Linux Distros to a single USB drive/Pendrive/Flash drive and boot from it.