anonyMous was a comedy troupe that Joe Hawley founded in the fall of 2002 while attending the University of Michigan. Rob was also a member, as were a couple other friendly faces we see scattered around Tally Hall's videos, such as Rick Lax.
In fact, many of Tally Hall's earlier videos were actually taken from a movie called Sargasm, which was a 45-minute long compilation of anonyMous sketches, all directed by Joe Hawley and released in the spring of 2003. The film was shown at the Michigan Theater and was described by Joe as like "‘Saturday Night Live,’ only funny."
Most people became familiar with anonyMous after watching the music video for Break It Down, which is often credited to Tally Hall, even though it technically is not a Tally Hall song. However, in 2006, Tally Hall did rewrite this song, adding in a chorus and basically made it into a standard pop song. They played it a couple times, but it quickly disappeared from their set. No word on if it will re-appear but it does seem to be a favorite amongst fans.