Open Container Initiative - "Creating open standards around container technology". Home for the OCI runtime, image, and distribution specs.
Docker "helps developers bring their ideas to life by conquering the complexity of app development."
Moby - "An open framework to assemble specialized container systems without reinventing the wheel."
containerd and its satelite projects.
Containers - "Open Repository for Container Tools." Heavily Red Hat backed.
GoogleContainerTools is home for distroless, kaniko, Jib, etc.
rootless-containers - "Bringing rootless containers to the masses."
CNI is home for the CNI specification and various networking plugins.