The two main religious movements at the time of the Buddha were those of the brahmans and the samanas. I have not been able to check it but I think our word shaman is related to the Pali samana. The brahmans adhered to age old Vedic religion and considered the Vedas to be the ultimate spiritual authority. However, the more forward looking brahmans of the day were starting to doubt the efficacy of Vedic rituals and give more attention to ethics and meditation. In particular, they were increasingly uneasy about Vedic sacrifices which involved the slaughter of animals. However these and other teachers still saw themselves as still within Vedic orthodoxy and so it is more correct that they were the founders of schools rather than sects.