Mennonites, Amish, Hutterites, German Baptist, Dunkards, Schwarzenau, Brethren are amoung the major groups that all descended from the Anabaptist movement in Europe. Like any group which desires to follow the Bible, and lacks a strong human hierarchy to enforce one way they are prone to legalism and numerous splits. I wouldn't call the Mennonites the source group, but they are probably the largest. Although the Amish may well eclipse them in numbers.
There is a very large diversity of practice amoung the Anabaptists. Some are very distinctive and in many ways operate a lot like the early church and some have a lot of high church influence.
Basically they are the adult baptizers from continental Europe. The other American groups who baptize adults mostly come from Great Britain (usually England or Scottland). Unlike the English groups, the Anabaptists tended to keep more to the old traditions (excluding the more liberal Mennonites); why, I am not entirely certain of.
That they are, we can learn a lot from them. A lot of that success comes down to large families, being separate from the world, rejecting divorce, and being willing to excommunicate members who digress from their standards. In contrast, even amoung American churches that teach no divorce, they are quick to make excuses for any women who nevertheless chooses to do so and believe any wild tale she spins.
Unfortunately their separateness plus the quiet of the land approach to avoiding persecution means they have entirely given up on evangelism.
I suppose given their strong top down church authority, which is exclusively male, they have kept the women in check. Something the American church failed to do.
In a way you could look at them like a modern tribe, but one where tribal government and religion merged. That would go a long way in explaining how they have managed to withstand being subsumed into the consumerism beast, something almost no other tribe the world over has managed to do; despite being right in the belly of the beast.
