This is a real Kubernetes v1.37 control plane. Not a simulator. kube-apiserver, kube-controller-manager, kube-scheduler and kubectl are the upstream Go code, compiled to WebAssembly into one binary. The only replaced part is etcd: a small in-memory implementation of the etcd v3 API. Everything runs in your browser tab. Reload the page and the cluster is gone.
A control plane without nodes is boring. Type join and start the printed docker run command. The container runs a kubelet and containerd and connects to your browser with WebRTC. Then kubectl get pods -A shows flannel, kube-proxy and CoreDNS on a real node.
The boot takes around 15 seconds. WebAssembly in the browser is single threaded, so the whole control plane shares one CPU core. The source is in the blog repository.