While there is a history of atheist/agnostic thought within the Hindu philosophical tradition, have there ever been actual communities of atheist/agnostic Hindus?
There have been 4 main non-theistic(nirīśvara-vāda) schools in Hinduism:
- Purva Mīmāṃsā
Cārvāka was a materialistic non-theistic school. I.e they believed in only pratyakṣa(perception) pramāna(valid means to knowledge). This puts them in the material realm. A simplified view of their philosophy would be : "If you can see something which exists, it must be true or else it is false. I cannot see Brahman, so Brahman does not exist. I can see this tree, so this tree exists."
The first 3 are spiritual non-theistic schools. I.e they believe in more than just perception and extend valid means of knowing to meta-physical realms. These are similar to Buddhism & Jainism in rejecting a creator God but not rejecting the meta-physical realms which are beyond human perception(similar only in this aspect).
Cārvāka is not usually grouped along with Sāṃkhya, Purva Mīmāṃsā & Yoga despite all the 4 being non-theistic is because Cārvāka doesn't consider śabda pramāna(Śruti or Vedas) to be valid means of knowledge, while the others do. They(the former 3) interpret Vedas non-theistically, mainly as a source of ethics(Karma, Dharma) only and don't believe in creator & sustainer God.
- Mīmāṁsā, as mentioned above, is a non-theistic form of Hinduism. It states that the gods are not real, only existing as myths and stories. They argued that they had no need for a God or Gods to validate the regular rituals they engaged in. It was explained by Indian Nobel Prize-winner Amartya Sen, in an interview with Pranab Bardhan for the California Magazine:
In some ways people had got used to the idea that India was spiritual and religion-oriented. That gave a leg up to the religious interpretation of India, despite the fact that Sanskrit had a larger atheistic literature than what exists in any other classical language. Madhava Acharya, the remarkable 14th century philosopher, wrote this rather great book called Sarvadarshansamgraha, which discussed all the religious schools of thought within the Indian structure. The first chapter is "Atheism" – a very strong presentation of the argument in favor of atheism and materialism.
One of the reasons for this interpretation is something found in other nontheistic versions of Hinduism: a nontheistic interpretation of the Bhagavad Gita, specifically passages like "The supreme Brahman is without any beginning. That is called neither being nor non-being,", which Indian philosopher Adi Shankara interpreted as the supreme Brahaman being close to a borderline non-existential being that could only be talked about in terms of negating all attributes or 'Neti neti'.
- Samkhya philosophy is another nontheistic branch of Hinduism and based around dualism. It states human development constituted two independent principles: puruṣa ('consciousness' or spirit); and prakṛti, (cognition, mind and emotions, c.q. nature or matter). It also gets its non-theistic approach from Rigveda's vague explanation of the formation of the universe and explanation of the existence of life:
Seven Sisters utter songs of praise together, in whom the names of the seven Cows are treasured. Who hath beheld him as he [Sun/Agni] sprang to being, seen how the boneless One [spirit] supports the bony [body]? Where is the blood of earth, the life, the spirit? Who will approach the one who knows, to ask this? — Rigveda 1.164.2 - 1.164.4
This branch of Hinduism also gets its stance from early writings in the Katha Upanishad which speculates nothing is above Purusa (spirit) and that said spirit is unknowable, independent, and does not directly dictate human behavior or morality or how being should be like 'gods' in the Western tradition sense:
Higher than the senses, stand the objects of senses. Higher than objects of senses, stands mind. Higher than mind, stands intellect. Higher than intellect, stands the great self. Higher than the great self, stands Avyaktam(unmenifested or indistinctive). Higher than Avyaktam, stands Purusha. Higher than this, there is nothing. [It] is the final goal and the highest point. In all beings, dwells this Purusha, as Atman (essence), invisible, concealed. —Katha Upanishad 3.10-13