NaaS:

Namespace as a Service.

• Capsule
• Kiosk
• HNC

AaaS

API as a Service.

• KubeZoo

CPaaS:

Control Plane as a Service.

• Kamaji

CaaS:

Cluster as a Service.

• VCluster
• Virtual Cluster
• kcp
• KubeSlice

Other:

• Kubernetes Multi-Tenancy WG
• Kubernetes benchmarks for multi-tenancy

Blogs:

• https://towardsaws.com/kubernetes-multi-tenancy-approach-b0f58d615971
• https://dev.to/ashokan/naas-conclusions-for-now-6oo