kcp is the Kubernetes API machinery without Kubernetes. It is a fork of kube-apiserver and the surrounding controller libraries, stripped of pods, nodes, and the rest of the container-oriented APIs, and extended with a native multi-tenancy concept called workspaces. The result is a control plane that serves CRDs and the full watch/list/reconcile machinery you know from Kubernetes, but as a general-purpose declarative API platform rather than a container orchestrator.
Workspaces are the headline feature: a kcp server can serve effectively unlimited logical clusters, each with its own API surface, RBAC, and resource graph, all sharing one etcd. APIExports and APIBindings let one workspace publish a set of CRDs and another workspace consume them, with a controller-facing “virtual workspace” endpoint that presents bound APIs across many tenants at once. This makes it possible to build a SaaS where every tenant thinks they have their own Kubernetes-style API for your product, without you running a cluster per tenant.
Originally a Red Hat research project, kcp is now a CNCF sandbox project. It is not a Kubernetes distribution and you cannot run pods on it; think of it as “the API layer of Kubernetes as a platform-building toolkit,” in the space of Crossplane, Upbound Spaces, and the internal developer platform ecosystem.