Flux is a set of continuous delivery tools designed to keep Kubernetes clusters synchronized with sources of configuration. As a CNCF graduated project, it implements the GitOps pattern using a set of composable Kubernetes controllers that react to changes in Git repositories, Helm repositories, and OCI registries.
Unlike ArgoCD's monolithic approach, Flux is built as a collection of specialized controllers (source, kustomize, helm, notification, image-automation) that can be used independently or together. This makes it lightweight and flexible, fitting naturally into existing CI/CD workflows.
Flux is completely free and open source under the Apache 2.0 license. Commercial support and enterprise features are available from Weaveworks (now maintained by the CNCF community).