I'd like to use this thread to outline the findings of my studies in the history of universalism.
On the Tentmaker article, Tracing Universalist Thought Through History, the influential mystic, Jacob Boheme is incorrectly listed as having been a universalist. The Christian Universalist Association website claims the same thing.
However, in fact, his version of spiritual eternal torment was the whole linchpin of his theosophic musings. Though he does allow that seeing the joy of the elect might be a comfort to the damned.
Johann Arndt is another influential writer listed on Tentmaker as having been universalist. In reading his writings, I can't find anything to support this conclusion, and he actually seems to have been a believer in eternal torment. Like Boheme, his Hell seems to have been spiritual.
On the flip side, many of the Pietists, mostly of the radical wing, were universalist, and I don't see this emphasized as much as it could be. Bengal, Phillip Jacob Spener, Ernst Christian Hochman von Hohenua, Alexander Mack, etc, all were closeted universalists.
Alexander Mack and the German Baptist Brethren, when they emigrated, were the first organized church in America to be universalistic. However, they mainly held this belief in private. In 1795, a GBB preacher in the Carolinas began openly preaching Hosea Ballou's version of ultra-universalism (no punishment and chastisement after death). This perturbed the Brethren, and they kicked out all the congregations who subscribed to ultra-universalism (1,000-2,000 members) and forbade the open declaration of universalism.
It is still permissible to hold a belief in the "restitution of all things" privately in some of the groups descending from the GBB, though not the groups influenced by fundamentalism and evangelicalism.