Open Source Virtual Machine
Virtualization is where infrastructure economics get decided quietly, because a per-socket or per-core license tax turns raw consolidation - the whole reason you virtualize - into a recurring cost that scales with the very density you were chasing. The open source hypervisors here give you that same isolation and live migration without a licensing meter on your CPUs, so you can pack workloads as tightly as the hardware allows and keep full control over the layer everything else runs on.
Podman
Daemonless tool for managing OCI containers, images, volumes, and pods with a Docker-compatible CLI
QEMU
Emulates and virtualizes whole machines, running an OS or binary built for one architecture on another
KubeVirt
Runs virtual machines as native Kubernetes objects, so VMs and containers share one cluster and one API
OpenStack
Open source cloud computing infrastructure for computing, networking, and storage resources through programmable APIs
Cloud Hypervisor
Rust virtual machine monitor for cloud workloads, with minimal device emulation and a small attack surface
Incus
Runs full Linux systems as either system containers or virtual machines from one REST-driven manager
Harvester
Hyperconverged infrastructure on bare metal that folds virtualization and distributed storage into Kubernetes
LXD
Canonical's manager for running full Linux systems as system containers or VMs, from one host to a cluster
Apache CloudStack
Open source IaaS platform for deploying and managing large networks of virtual machines