Kubernetes is by far the most popular container orchestrator out there. Many public cloud providers are now adopting it as the de facto container orchestrator; for instance, Azure with its Azure Kubernetes Services (AKS), Amazon Web Services with elastic container service for Kubernetes (EKS), and Google Cloud with Google Kubernetes Engine (GKE). Most of these solutions are managed, abstracting the management plane for the user for ease of use, and adopting cloud-native solutions such as integration with public cloud load balancers and DNS services.
Kubernetes sits in the middle of a platform as a service (PaaS) solution and an infrastructure as a service (IaaS) solution because it provides you with a platform to run your containers and manage your data, but it still lets you provision software-defined infrastructures such as load balancers, network management, ingress...