I am aware of only the Sahajiya-Vaishnavas (a tradition that heavily borrows from Gaudiya Vaishnava philosophy), prevalent in Bengal so consider this a partial answer. There are both Vamachara and Dakshinachara Sahajiyas. Famous Sahajiyas include the poets Chandidas, Vidyapati and Jayadeva.
The followers of this sect have been historically being ridiculed and considered taboo by the society, even from the Gaudiya Vaishnava community. As a result, most followers do not reveal their identity and carry out their practices in secret, even till today. Interestingly, according to the Sahajiyas, Chaitanya Mahaprabhu too engaged in Vamachari practices, particularly maithuna with the daughter of His famous disciple, Sarvabhouma Bhattacharjee. Sahajiyas have been condemned by both Bhaktisiddhanta Saraswati Thakura and A.C. Bhaktivedanta Swami Prabhupada in their works (You can read all the quotes of Prabhupada on Sahajiyas here).
According to Wikipedia:
The Vaishnava-Sahajiya sought religious experience through the five
senses which included human coupling and sexual love. Sahaja
(Sanskrit: “easy” or “natural”) as a system of worship was prevalent
in the Tantric traditions common to both Hinduism and Buddhism in
Bengal as early as the 8th–9th centuries. "Sahaja" was evident in the
teachings and poetry of Mahasiddha Saraha (c.8th century CE, Bengal,
Nalanda).
The tradition used the romance between Krishna and Radha as a metaphor
for union with God, and sought to experience that union through its
physical reenactment. It teaches that the ideal way to understand the
union of humanity is to transcend the profane aspects of sexual
intercourse and experience it as a divine act.
The Vaisnava-Sahajiya creed is a synthesis of these various
traditions. The Vaisnava-Sahajiyas operated in secrecy because their
sexual tantric practices were viewed with marked disdain by other
religious communities. In their literature they adopted an enigmatic
style employing substitutions and correspondences that has come to be
known as twilight language. Little is known about their prevalence or
practices.
The cult was centered in Bengal. It began in the 16th century,
although predecessors existed as early as the 8th century in the same
city. The founder is generally thought to be Baru Chandidas, who lived
in the 14th century. In order to avoid unwanted attention, the group
spoke of its activities in cryptic language.
Members of this lineage enacted the 'group in a round' Ganachakra or
circle dance now known as the Rasa-lila of Krishna. It is a mystery
religion rite, wherein the followers participated in a rite of
communion, trance possession, and nondifference or nonduality with 'deity'.
From Banglapedia:
Its followers believe in the sahaja or simple way to feel the sahaja
or innate reality that is present in every animate or inanimate
object. According to Sahajiya philosophy, along with an external form,
every object also has an internal form. This internal form is the
eternal, otherwise known as sahaja. To feel the sahaja is to feel the
internal eternity in one's self. The whole range of animate and
inanimate objects can be felt by experiencing this internal form. The
followers of this cult think that a simple, direct way is the best
means to experience this feeling.
What goes in favour of human nature is the sahaja (simple) and what
goes counter to it is vakra (crooked). The attainment of the self
through that which is in accordance with human nature is the objective
of Sahajiya philosophy. The Sahajiya believe that the object of
worship is knowledge, and this knowledge resides within the self, not
outside it. They believe that this knowledge cannot be acquired
through study and books, but only apprehended through the advice of
preceptors and the indoctrination of sahajasadhana.
The Sahajiya emphasise the importance of the body. They believe that
the body embodies the universe and attainment of the self can only be
made through bodily love. Literature based on Sahajiya philosophy is
classified as Sahajiya literature.
And this is what Dr. Satyanarayana Dasa Babaji, a renowned modern Gaudiya Vaishnava Guru and the founder of the Jiva Institute of Vaishnava Studies, says abouts Sahajiyas:
There was a Buddhist sect called Sahajayāna, besides the Mahāyāna and Hīnayāna sects, which was popular in the Eastern part of India before the appearance of Mahāprabhu. They followed the Tantric practice of trying to elevate their consciousness or raise the Kundalini with the help of a female partner. The purpose was not to enjoy sex as is misunderstood by many. Some sects of Tantra still practice this and it has unfortunately become the popular understanding of the Tantra practiced in the West.
When Mahāprabhu became popular in Bengal and Orissa, many of these Sahajayānis took to Gauḍīya Vaiṣṇavism being influenced by Mahāprabhu. They subsequently mixed their Sahajayāna practice into the philosophy of Mahāprabhu. They believed that Goloka Vṛndāvana exists in the physical body and love of Kṛṣṇa is dormant within the ātmā. This love can be manifested in the most natural way (sahaja) in the association of a female, especially a woman who is not one’s wife (parakīya) as the male mind is naturally attracted to women other than one’s wife.
Sahajiyās consider Caitanya-caritāmṛta as one of the most important books of their school and claim that even Caitanya Mahāprabhu had a female partner. According to them, the daughter of Sārvabhauma Bhattācārya, Ṣāṭhī, was Mahāprabhu’s partner. This was the reason behind Ṣāṭhī’s husband, Amogha, being upset with Mahāprabhu when He came to Sārvabhauma Bhattācārya’s house to take lunch prasād. (CC Mad 15.245-248)
Similarly, in their books the sahajiyās give the names of the female partners of all the Gosvāmīs of Vrindavan. They consider this knowledge to be very esoteric. Therefore most of their literature has never been printed. I have a collection of such manuscripts in my personal library.
It is also worthwhile to note that unlike most Vaishnava traditions, Sahajiyas did not stress on vegetarianism or even follow the rules of Ekadashi so even though maithuna was considered the most important practice, partaking madya and mansa was definitely included in the tradition.
One of the most famous Sahajiya text is the Radha Tantra. Unfortunately, the text has not been translated in English. You can read it in Bengali here.
