Traditionally, operating systems (OS) installed directly on physical hardware have unfiltered access to the underling system hardware, which they trust by default. In contrast, when deployed inside virtual machines, this access can be mediated at the hypervisor/host level, enhancing the security of the overall system by allowing the user to distrust parts of the hardware stack, a vision that is implemented thorougly by the QubesOS, which Phyllome OS draws inspiration from.
Despite these advantages, most individuals don't use a virtual machine as their main desktop OS. One of the reasons is that granting a virtual machine 3D capabilities — a must-have to achieve optimal performance on any desktop environment — is still difficult, prone to errors, and risky from a security standpoint as it increases the attack surface of the overall system.
The goal of Phyllome — which is in its very early stages — is to develop and distribute a KVM/QEMU-powered Linux distribution built on a small set of software and that will allow the virtualization of 3D accelerated guest operating systems out-of-the-box, including non-UNIX ones, while offering better security and privacy than OS installed directly on physical hardware.
According to the Wiktionnary, phyllome means
a foliar part of a plant; any organ homologous with a leaf, or produced by metamorphosis of a leaf.
The alpha version has been released in November 2021.
Phyllome OS is currently a one-man effort, but couldn't exist without the work of thousands of open-source contributors.
For a couple reasons :
Development velocity
Piggy backing
Extensibility
Sane security by default