http://crossplane.io is a popular open source Cloud Native Computing Foundation project that provides a framework to help you build your own opinionated cloud native control plane — complete with all of the policies, best practices and configurations that are important to your organization. You can think of this framework as the “building blocks” for creating specialized and customized platforms.
https://docs.crossplane.io/v1.10/concepts/terminology/#managed-resource are the next layer up and are how Crossplane brings this real-world infrastructure into the control plane to expose them as extensions to the Kubernetes API.
Crossplane is all about extending the control plane with new types that represent real-world infrastructure and services.
https://www.upbound.io/ created the Crossplane project in 2018 with a vision to take the cloud native space to a new level.