RegShape (from REGistry reSHAPE) is a CLI tool and a Python library for manipulating artifacts in an OCI registry. While there are many other tools that can do this (see ORAS, regclient or Google's crane), the goal of RegShape is to provide a flexibility to manipulate the requests with an intention to break the consistency of the artifacts.
You should be able to use RegShape similarly to the tools above, but you can also use it in expert mode where you can manually craft the requests to the registry and try to break it. This is useful for testing the registry implementations or the security of the registry.
RegShape is written in Python and offers Python libraries that can be leveraged to build your own tools. The CLI tool is built on top of the libraries and uses click framework.
Note: The tool is still in early development and the API is not stable yet.