KVM Kernel-based Virtual Machine
Linux kernel module that turns the kernel into a Type-1 hypervisor. Combined with QEMU for full hypervisor functionality. Merged into Linux 2.6.20 (2007).
Avi Kivity (Qumranet, then Red Hat) created it. Uses hardware virtualization (Intel VT-x, AMD-V). Effectively drives the entire open cloud — AWS Nitro (since 2017), Google Cloud, OpenStack, Proxmox. Performance near native. libvirt + virsh + virt-manager are common admin tools. Competitors: Xen (older, still at AWS for some instance types), VMware ESXi (commercial).