Religion: Hinduism and Buddhism were very similar with reincarnation, but differed because Buddhism disagreed with caste. Hinduism was more popular because of the Brahmans and the Guptas supporting it strongly. Hinduism also showed more of a mystical side.
Kamasutra: Laws of love, 4th century CE.
Classical stories were often secular, and Indian drama also flourished with romantic themes.
Science and Mathematics: Astronomy and Medicine. Calculated length of solar year, understood rotation of earth on it's axis, predicted and explained eclipses, developed a theory of gravity, and identified seven planets. Medicine was hampered by religious constraints to dissect, but still bone setting and plastic surgery was improved.
Mathematics: Number system we use today. Concept of negative numbers, zero, decimal system, square roots, table of sines, and computed value of pi more accurately than Greeks.
Art: Stupas and stylized, lively sculptures and paintings.