Private Registries
OpenTofu, by default, uses the public registry at registry.opentofu.org. However, organizations may have a need for a private registry for modules or providers that need to be kept private.
There are several project that implement the terraform registry API, aimed at providing this functionality of hosting a private registry. They are also compatible with OpenTofu. Some of the projects only support providers, some only support modules, and some support both. Choose one that is appropriate for your use case.
List of Private Registries
The list of projects is available at awesome-opentofu.
How to Use
Follow the documentation provided by each registry to integrate it with your OpenTofu projects.