Vedic Tradition :- The Vedic background of India's religious traditions is a source of lively scholarly discussion. Neither the dating of the earliest practices nor the ethnic character of the earliest practitioners is certain. However, the prestige and influence of Vedic tradition is generally agreed.
Hinduism :- The mega-tradition of India (or, some would say, the artificial construct created by Western scholars to interpret religion in India). No founder or single, central authoritative institutions. Possibly the most ancient of human traditions. Requires a fairly steep learning curve to gain competence in understanding Hinduism due to the complexity, multiple classical languages, and mass of information that resists simple classification -- but is fascinating and well worth studying.
Jainism :- Like Buddhism, an ancient ascetical tradition. The last great master was Vardhamana, who was iven the title 'Mahavira" (Great Hero) and was believed to be the last of the Tirthankaras (those who had crossed-over or "forded" the ocean of earthly existence and had reached the ultimate realm of eternal bliss). Again like Buddhism, Jainism split into subtraditions, and gained many non-monastic followers. Unlike Buddhism, Jains generally did not travel outside India until recent times. Currently there are probably about four million Jains worldwide, all but about 200,000 in India.
Buddhism :- Established in northern India about 2500 years ago in response to the life and teachings of Gautama Siddhartha who was given the title 'Buddha' or awakened-one, the tradition has spread throughout the world and has subdivided into numerous distinct groups. Although monasticism was a major aspect of early Buddhism, the tradition has both monastic and non-monastic followers.
Islam :- The youngest of the Abrahamic traditions, it dates from the seventh century of the CE calendar, and closely identifies itself with the prophetic strands of Biblical tradition. However, it has highly developed legal and mystical traditions of its own as well. And it is a dramatic example of a "religion of the book" in which the Qur'an is widely regarded as the full, final revelation of the One Creator of the universe to his last and final prophet, Muhammad. The second (perhaps even first) most populous religious tradition in the world.
Sikhism :- The tradition that developed from the teachings of Guru Nanak and his nine successors. The lineage of human spiritual masters ended with Guru Gobind Singh and subsequently the teaching authority passed to the Guru Granth Sahib -- a highly honored scripture -- and the collective membership of the baptisted order within Sikh tradition that was established by the last of the human masters -- the Khalsa Panth. There are about fourteen million Sikhs worldwide, most of them still living in or near the Punjab state of northern India.
Zoroastrianism :- In the last millennium BCE, this tradition probably was at the peak of its influence as a major religion of the Persian Empire. It was overcome by the rise of Islam, and has been preserved mainly through immigrants to India known as Parsi (= Persian) and more recently through their small number of descendants who live not only in India but also in other countries worldwide.