Piano Roll

A pianoroll is a horizontal based note-sequencer, where notes are drawn on horizontal base-line rather than in vertical columns like a tracker does.

A pianoroll has a timing advantage above the average tracker. Though Renoise now records note-delays during play/record mode, so currently there is a good compromise between live recording and pattern sequencing, which most musicians in the Cubasis world only prefer for sequencing percussion and the like.

(image taken from the Brahms Open Source midi-sequencer page)