A spiritual brotherhood certainly worthy of being better known is the Dominican-affiliated Angelic Warfare Confraternity.
The Confraternity is under the patronage of the Angelic Doctor, St. Thomas Aquinas (+1274AD). Indeed, it takes its name from the episode in the life of St. Thomas when, in defense of holy purity, he drove off a woman-of-ill repute that his brothers had sent to his room to tempt him away from chastity. At that point he was gird with a cord by angels and shielded from further attacks against purity.
The Confraternity seeks to encourage holiness and purity in its members under the patronage of St. Thomas Aquinas and the Blessed Virgin Mary. To that end, the members pray for one another, and wear the cord and/or medal of St. Thomas.
The Angelic Warfare Confraternity was approved as a Confraternity of the Order of Preachers (Dominicans) for the whole Church by Pope Benedict XII in 1727AD.
Pope Pius XI, in his encyclical letter, Studiorum Ducem, on St. Thomas Aquinas, 25, writes:
"Inasmuch, therefore, as We see the majority of young men, caught in the quicksands of passion, rapidly jettisoning holy purity and abandoning themselves to sensual pleasures, We instantly exhort you, Venerable Brethren, to propagate everywhere, and particularly among seminarians, the society of the Angelic Militia founded under the patronage of Thomas for the preservation and maintenance of holy chastity and We confirm the privileges of pontifical indulgences heaped upon it by Benedict XIII and others of Our Predecessors. And that the Faithful may be persuaded the more eagerly to enroll in this Militia, We grant members of it the privilege of wearing instead of a cord a medal round the neck impressed on the obverse with a picture of St. Thomas and the angels surrounding him with a girdle and on the reverse a picture of Our Lady, Queen of the Most Holy Rosary." [N.b., Pius XI, Studiorum Ducem]
Members of this brotherhood include, "St. Aloysius Gonzaga, Blessed Pier Giorgio Frassati, Blessed Columba Rieti and Blessed Stephana Quinzan (who actively promoted the Confraternity among women)."
The website of the Confraternity can be found here: Angelic Warfare Confraternity
This is the site where one can purchase the necessary items for membership: New Hope Publications
Certainly a Confraternity emphasizing the Angelic Doctor, whose sublime writings do so much to increase our understanding of the Faith, and Holy Purity, so ignored and ridiculed in our world, is of great contemporary relevance.