Geert Groote was a well-connected and comfortably provided cleric of Deventer who, in the mid 1370s, gave that up after an illness and a period with the Carthusians. He took deacon's orders, obtained a licence to preach in the diocese of Utrecht, and preached against clerical concubinage and simony to very large audiences until the licence was withdrawn. He gave over part of his own house in Deventer to a group of devout women living in common, and after his death in 1384 his followers organised themselves as the Brethren and the Sisters of the Common Life.
The arrangement was the point and the problem. They lived together, pooled their earnings, obeyed a rector and kept a rule of life, but they took no vows, wore no habit and were free to leave, which meant they were not a religious order and could not be governed as one. That drew repeated accusations of running an illicit order under another name, and the houses had to defend their legal position more than once.
The Windesheim congregation, founded in 1387 as a house of Augustinian canons regular, was in part the answer to that: an unambiguously canonical form for those who wanted one, which grew into a large congregation of monasteries and carried the movement's spirit inside conventional structures.