Azure released AKS in October 2017, providing managed Kubernetes service for free to Azure users. Unlike AWS, which charges for master node management fee, Azure only charges for Kubernetes virtual machine (VM) usage. Similarly to AWS, however, Azure originally had pushed an ECS-equivalent service Service Fabric. Although there is a common misconception that Azure is only compatible with Windows-stack (.NET, C#, etc.), AKS works seamlessly with Azure-hosted Windows and Linux VMs.
Despite an earlier release date than Amazon, AKS seems to lag behind Amazon EKS and GKE in terms of Kubernetes upgrade, support, and adoption numbers. While Amazon EKS and GKE supported Kubernetes 1.10.x relatively quickly since its release, AKS only recently started supporting it. Additionally, unlike Amazon EKS and GKE, master nodes are not offered in high-availability (HA) mode. Considering pre-existing usage of Kubernetes on AWS and GKE’s early lead in Kubernetes development, community involvement in AKS seems to be low so far.
That is not to say that AKS features are lagging in all domains. AKS is currently the only provider for an incubator feature called Service Catalog, which allows for applications inside Kubernetes to use externally managed services (e.g. Azure databases). Microsoft has also been active in maintaining a popular Kubernetes package manager, Helm.