A QuadBook Pro is an Intel-based Macbook Pro configured to NATIVELY boot the 4 major operating systems - MacOS, Windows, Linux, and ChromeOS. Through the power of a bootloader known as rEFInd, you're able to boot into the OS of your choice.
There are numerous computers out there that can multiboot various OS's, but the 2012 to 2019 Macbook Pros require far less "hacking." In fact, they are the only laptops that are more or less supported to multiboot, making them the most stable.
Sure, these older Macbook Pros are a little outdated, but they more than hold their own against today's top-of-the-line bargain computers, and, perhaps more important, they'd likely outlast them too. But why would anyone want one, you might be asking?
There are actually countless reason. Maybe you're a Mac addict, but have paid software (or a classic game) that only runs on Windows. Or maybe you're a network administrator and know somethings are easier handled in Linux. Or maybe you just want to show off.