Tibet’s “Dark Age” was perhaps the high point for the ngakpa tradition, and may have important implications for Buddhism’s future. Jacob Dalton has done some of the most interesting research on non-monastic Tantric practice in the Dark Age.
A talk he gave on the subject two years ago is available as a “webcast” (online audio recording/podcast). (Click on the speaker icon on the linked page to listen.)
His title was “Rethinking Tibet’s Dark Age: Demons, Tantras, and the Formation of Tibetan Buddhism.” From the talk description:
Traditional accounts have obscured the more positive aspects of the period. Freed from the watchful eyes of the imperial court and the monastic orthodoxy, Tibetans of the late ninth and tenth centuries were able to make Buddhism their own. The themes, the imagery, and the strategies they developed during these inchoate years formed the cultural foundations upon which Tibetan Buddhism would be built. Only by excavating these foundations and shedding some light on this “dark age” can we gain a clear appreciation of the Tibetan adaptation of Buddhism.