Eastern Orthodox ? While they are considered a third branch of Christianity they seem to have kept it quiet.
No Eastern Orthodox were very similar to the RCC in teaching. Most of these kind of churches I mean got nick named 'ana-baptist'. They didn't have that name for themselves, without denominational names. They were given names according to main leaders in their groups. Not all ana-baptists were sound in the faith, but among them were groups that stuck to a pure faith before the RCC and the Reformers.