I did remember one aother group however this group splut before the Watchtower was even formed. When C.T. Russell, Nelson Barbour and John Paton formed an alliance. Barbour began republishing the Herald of the Morning, Russell and Paton wopuld travel to encourage the subscribers and do back calls.
One of the men Russell met a minister by the name of A.P. Adams who seemed very interested in the message, and so he supported the group. However around 1878, Russell and Paton left Barbour, formed the Watch Tower, later Paton Left Russell and formed the "The Larger Hope publishing Co, and began publishing "The World's Hope" magazine. Adams who never joined the Watch Tower or stayed with Barbour began publishing "The Spirit of the Word." The magazine only ran for about a year, he also published a few booklets. Yet somehow Adams' following as as diverse as C.T. Russell's. There are dozens of groups and individuals who believe Adam's was a messenger of the Lord. His writings can be read online, just do a search.
One of the "offshoots" of Adams' would be A.E. Knoch who published "Unsearchable Riches". It is not known if he really was an offshoot, but many seem to lump them together as well as Paton, because of their universalist views. While Adams, Paton and Knoch believed ALL wold be reconciled, Russell believed ALL will be given the OPPORTUNITY to be reconciled.
RR