My mother’s people always referred to January 7 as “Old Christmas.” They were/are Moravian and some Lutheran. Of course, the Orthodox who originally proselytized the Moravians are by now a dim memory, known to few outside seminarians and scholars. Many no longer even realize they’re the spiritual heirs of Jan Hus after that.
Correct. The Anabaptist Branch of Christianity does not consider themselves a part of the Protestant movement because they predated it by centuries. Most branches of Anabaptists do not recognize the authority of the Council of Nicea, unlike traditional Protestantism. Many, however, accept its conclusions, some out of genuine belief, some out of tradition as a price to be paid to be accepted into the mainstream of Christianity and end persecution.
Jan Hus, while the best known of their spiritual leaders and martyrs was, by no means, the only one.
During the religious wars in Europe in the late 16th and early 17th century, the one thing the Catholics and Protestants agreed upon were that the Anabaptists were heretics, resulting in their wanton and senseless slaughter.
This was a primary motivator for many of their branches to move to America and, eventually, why the Roger Williams model of religious freedom won out over the Mather family model of puritanism.
The Mennonites actually maintain a website which details the history of the various Anabaptist movements, including one which practiced polygamy.
The Quakers were probably the largest and best known branch of the Anabaptist movement though, depending on which particular Quaker you talk to, they may consider themselves an entirely separate movement. Some have even evolved into extreme secularists, using the tradition of opposition to state sponsorship of any religion as a club to impose their own view of state secularism as a de facto religion-- sort of the same thing which has happened to the secularization of well-known Protestant sects such as the ELCA, Methodists and Presbyterians.
BTW, I beleive the tradition of "Old Christmas" dates from refusal to accept the Gregorian calendar. Most of Protestant Europe viewed it as a Catholic invention (which it was, but it was also accurate) but gradually asccepted it over the 17th Centrury. The United Kingdom held off acceptance until early in the 18th Century. I beleive the date is not fixed as it has been celebrated on January 6th in some years, but will be January 7 in 2012. It may have something to do with Leap Years. I'd have to look it up.