Qubes

Qubes OS, commonly known as Qubes, is a free and open-source desktop operating system that prioritizes security through compartmentalization. It uses virtualization to separate tasks into isolated virtual machines (VMs), so a compromise in one VM does not automatically compromise others. The design aims to enable safe handling of sensitive data and reduce the impact of zero-day exploits.

Qubes runs on commodity x86-64 hardware with hardware virtualization support and uses the Xen hypervisor to host multiple VMs. The user environment is built from different types of VMs: AppVMs run applications and user environments; TemplateVMs host the read-only root filesystem for AppVMs; Disposable VMs provide temporary, isolated environments for untrusted files; StandaloneVMs operate without template inheritance. Networking and security-critical functions are isolated in dedicated VMs, notably sys-net (networking) and sys-firewall (firewall). Inter-VM communication happens through a controlled RPC mechanism called qrexec and data sharing via a secure clipboard and file transfers.

Qubes provides a management layer and user interface to create, configure, and monitor VMs and domains. It uses TemplateVMs to supply software to AppVMs while keeping the AppVMs isolated from one another. The policy-driven approach supports fine-grained access control, such as preventing untrusted attachments from executing outside a disposable VM, and restricting how data can move between domains.

Qubes emphasizes defense in depth but has a steep learning curve and requires hardware with virtualization support and compatible drivers. It is used by individuals and organizations requiring strong isolation for sensitive workloads, though its hardware compatibility and performance can be a constraint for general-purpose users.