What are the most prominent Tibetan Buddhist texts that are only written in Tibetan script?

A lot of Buddhist texts come from Sanskrit or Chinese. I am looking at the Kangyur and Tengyur, and a few scattered others. But a lot of those are from Sanskrit and Chinese as well (or other languages, Pali, etc.). What books or groups of books/works can only be found in Tibetan script? _Whether or not it has been translated to other languages isn't important, the original language should be Tibetan though._ I am trying to mentally gather an image of how much reading would be required to gain the knowledge unique to Tibetan Buddhism.