The friends we visited in Indiana are Old German Baptist Brethren. The German Baptists are a plain people with an Anabaptist heritage. Established in 1881, their membership numbers roughly 5,000, with most of their brethren in Ohio and Indiana. The casual observer would probably mistake them as Amish, though they drive cars, use electricity, speak English rather than Pennsylvania Dutch, and wear fabric with patterns.
We attended church with our friends Sunday morning in Goshen, Indiana. It was a cross (sub) cultural experience. When our friends visited us in July they attended church (Brethren in Christ) with us on Sunday morning. Of course, the difference between our churches was noticeable--at their meeting the men and women sat on separate sides of the building, the service was formal and solemn, and the a cappella singing was slower than we could sing even if we knew the tune. The similarity, though less obvious, was more important--the service included the reading of God's Word and exhortations based on Scripture.
A helpful resource for understanding the similarities and differences between various Anabaptist groups, such as the Amish, Mennonites and Brethren, is Anabaptist World USA by Donald B. Kraybill and C. Nelson Hostetter (Herald Press, 2001).