The sequencer uses a 555 timer that feeds into a CD4017 decade counter. They wired in kill switches on each step to either change the time signature of the sequence or introduce syncopation. Each step has a potentiometer that can vary the frequency of the pulse or the control voltage.
Over the summer at ITP Camp, Mark and Ezer held a soldering workshop where the participants built sequencers of their own. The following day all the sequencers were linked together and they had themselves an electronic jam session.
Check out Mark’s site for more information and full documentation.