"Buddhism has the characteristics of what would be expected in a cosmic religion for the future: it transcends a personal God, avoids dogmas and theology; it covers both the natural & spiritual, and it is based on a religious sense aspiring from the experience of all things, natural and spiritual, as a meaningful unity."
Buddhism was originally an Agricultural Age (or Iron Age) Old Earth religion, founded on the Gondwana continent of Northern India by a member of a local royal house Siddhartha Gautama, who left his wife, children and his political involvements in order to seek truth as an ascetic mendicant. He studied the various spiritual teachings of his day, but ultimately rejected them and, through his own efforts and meditation, attained enlightenment and founded Buddhism in 2498 BT (535 b.c.e.). He promoted The Middle Way, rejecting both extremes of the mortification of the flesh and of hedonism as paths toward the state of Nirvana. He accumulated a large public following by the time of his death in his early 80's in 483 b.c.e. (2452 b.t.).
Two and a half centuries later, a council of Buddhist monks collected Siddhartha Gautama's teachings and the oral traditions of the faith into written form, called the Tripitaka. This included a very large collection of commentaries and traditions; most are called Sutras (discourses). The sect then underwent a number of schisms, the most prominent being the division into the Northern (Mahayana) and Southern (Hinayana, later just Theravada) Buddhism. Each of these, especially the more metaphysically creative Mahayana, was in turn divided into a number of different traditions. Many of these adherents have combined the teachings of the Buddha with local religious rituals, beliefs and customs. Little conflict occurs, because Buddhism at its core is a philosophical system to which such additions can be easily grafted.
Unlike most religions of Iron Age, Medieval, and Industrial Age Earth, Buddhism does not believe in a transcendent or immanent or any other type of God or Gods, the need for a personal saviour, the power of prayer, eternal life in a heaven or hell after death, and so on. Instead Buddhists affirm karma - the law of cause and effect and dependent origination; reincarnation: the concept that one must go through many cycles of birth, living, and death because of the effects of past karmic action, and Enlightenment or Liberation from the wheel of rebirth: after many such cycles, if a person releases their attachment to desire and the self, they can attain Nirvana.
Central to Buddhism are the Buddha's Four Noble Truths: the universality of suffering (dukkha), the cause of suffering (attachment or craving); the cessation of suffering (final liberation in nirvana), and the way to the cessation of suffering, the Eightfold Noble Path, viz.:
These basic principles remained in all forms of Theravada, Mahayana, Terrestrial Vajrayana, and Centauri Vehicle Buddhism. The more ascendic and otherworldly elements were however played down by Genetekker Vehicle exponents, who preferred to see enlightenment as something to be achieved here and now, rather than in a nirvana state.
There were originally three main "vehicles" or systems of thought within Buddhism which were geographically and philosophically separate. With humanity's migration into space many new vehicles developed. Each tradition in turn has many sects.
Southern Buddhism (known as Therevada or less politely Hinayana ("Lesser Vehicle") Buddhism) is the most conservative tradition. It spread to south east Asia - mainly in Burma, Cambodia, Laos, Sri Lanka and Thailand, and parts of Vietnam, and reached its greatest extent in the 15th to 20th centuries c.e (4th to1st centuries b.t.). Concepts and practices include: Dana - thoughtful, ceremonial giving Sila - accepting Buddhist teaching and following it in practice; refraining from killing, stealing, wrong behavior, use of drugs. Karma - the balance of accumulated sin and merit, which will determine ones future lives, The Cosmos - consists of billions of worlds grouped into universes and underworld and heavenly realms. Paritta - ritual chanting Worship - of relics of a Buddha, of items made by a Buddha, or of symbolic relics. Festivals (usually on the full moon); and Pilgrimages, particularly to Buddhist sites in Sri Lanka and India. Although Southern Buddhism spread briefly to the West and even acquired some adherents in the offworld colonies during the Interplanetary Age (the Metta Dhamma Loka Society based at Copernicus Habitat, Luna, at its height boasted a membership of 50,000 throughout the solar system and had an influence out of proportion to its size), most of its adherents remained on Earth. Following the Great Expulsion some of them set up small missionary centers in the Kuiper Belt, E Erandi and Tau Ceti III.
Mahayana or Great Vehicle Buddhism spread to China, Japan, Korea and much of Vietnam, during the 3rd to 6th centuries c.e. (17th to 14th centuries b.t.). It differed from traditional Buddhism with the addition of the Bodhisattva, the saviour figure who, although attaining Enlightenment, defers the bliss of Nirvana until all sentient beings are saved. It underwent severe repression during the 20th century c.e. (1st century b.t. and early 1st century a.t.) in China during the Cultural Revolution, from which it never really recovered (the post-Communist economic boom of the Chinese Free Enterprise Zones during the 21st century c.e. was hardly conducive to spiritual life). Mahayana Buddhism includes the T'ein-t'ai, Hua-yen, Pure Land, and Ch'an/Zen schools. In traditional Asia they celebrated New Years, harvest festivals, and five anniversaries from the lives of Buddha and of the Bodhisattva Kuan-yin, and engaged in Dana, Sila, Chanting. Worship and Pilgrimage. During the late 20th and early 21st century c.e. the Zen Buddhist tradition developed a respectable following in the West, particularly in North America. It also spread to some of the orbitals, especially Clarke and Roddenberry. The Orbital Tweaks were particularily attracted to Zen minimalism. Offworld Zen totalled 246,415 in the 2274 census. By the time of the Great Expulsion Mahayana had either disappeared on Earth or merged completely with other new and older religions.
Image from M Alan Kazlev
Vajrayana or Diamond Vehicle Buddhism 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 of the late 20th and early 21st century c.e. (1st century a.t.). Like Theravada and Mahayana, it spread to the West and established quite a respectable following, especially during the 2nd and 3rd centuries a.t. In some of the orbital habitats. Vajrayanist ideas were still popular among some baselines even as late as the Integration period.
Genetekker Vehicle Buddhism - Interplanetary age Genetekker development of Vajrayana/Buddhist Tantra that rejects the asceticism of orthodox Buddhism. First appeared in habitats around Jupiter in the Gengineer Republic where, along with Shakta and Shaivite Tantra, it was particularly popular among the tweak population. It still has a small following among a few Genetekker-descended groups in the Sol System and a few other old core worlds.
Centauri Vehicle and other Mahayana derivatives - Under the great religious visionary Boddhichittamaittreya III of the Federation era Proxima Centauri Colonies an Omegism-Zen hybrid - the so called Centauri Vehicle, became popular, and still retains some adherents on Boddhichittamaittreya habitat, as well as among colonies and biospheres throughout the galaxy. Most scholars acknowledge that the factionalised Centauri Vehicle sects of today bears little resemblance to Boddhichittamaittreya's original noble and inspiring teaching. Other Mahayana derivatives are KuanYinism (a cyborg devotional-meditation worship school) and Maitreyism (a baseline eschatological Omegist sect that identified the Maitreya Buddha with the Omega Exemplar; the famous Teilhard Maitreyists integrated this with Omegist Christianity); these faiths became locally quite influential as official religions of several minor Houses during the Empires Era and were widely worshipped in their domains.
The Bluesky Cult - derived originally from Buddhism, this sect promoted the concept of paraterraforming throughout the civilised galaxy
Peitho Buddhism - Neobuddhism developed by the Peitho school of Povenmire habitat, Rosselia (Sophic League) in 8700's. According to Peitho doctrine, the physical world is actually a hell realm of the true world. The graves of the exemplary dead are sacred places since they have a connection to the true world.
Buddha - In Buddhism and many other religions and memetics based on or inspired by it, one who is awakened, enlightened; one who is spiritually awakened, who has transcended limits of the relative self and attaiined to the true nature of reality.
Buddhabrain - An ISO, moon-node, jupiter-node, or nebula brain that has attained a state of holistic Enlightenment.
Buddhai - An enlightened ai (generally hyperturing or above), a transapient Mind that has transcended all toposophic levels, and indeed all phenomenal existence.