Vajrayana or Diamond Vehicle Buddhism
Image from M Alan Kazlev
Vajrayana, or "Diamond Vehicle" Buddhism was a major Old Earth Buddhist sect. It was the last form of Buddhism to develop on Old Earth, and was best known from Tibet. It incorporated Tantric elements and emphasized ceremony and ritual. It was bitterly persecuted and almost totally crushed in its homeland by the Chinese invaders during the Atomic Age and early Information Age. Like Theravada and Mahayana it spread to the West and established quite a respectable following, especially during the 21st and 22nd centuries and in some of the orbital habitats and microworlds.
Vajrayanist ideas were popular among human derived modosophonts even as late as the second Federation period.