True, I might have skimmed it. But even now that does not tell me much.

Best that I found was under Docs -> intro -> What is OpenTF?:

> OpenTF is an infrastructure as code tool that lets you define both cloud and on-prem resources in human-readable configuration files that you can version, reuse, and share. You can then use a consistent workflow to provision and manage all of your infrastructure throughout its lifecycle

That could have been on the frontpage somewhere. Or in the github description.