A drum machine, actually. But barring that, it seems like there should be a solution in drum sequencer modules such as Acidlab's Robokop, Twisted Electrons' Crazy8 Beats, or Erica's Drum Sequencer, all of which are specifically designed to function like drum machine sequencers. While I like and use the BSPs for various things, with one exception (triggering an ancient MXR Drum Computer with a blown sequencer section) I tend to use these as step sequencers, particularly in situations where I want multiple monophonic lines in asynchrony.