MusE: Linux Music Editor

start the pianoroll editor
click with left mouse button on ruler to set current position to the start position of your recording
set the Snap value to the step distance
set the Quantize value to the length of the notes to record
enter step record mode by pressing the "S" toolbar button
every click on the piano keyboard records a note with "Quantize" len and advances the current record position to the next "Snap" position
shift+click records a note without advancing the current record position
change the current position with the cursor keys
shift+space inserts a gap; all notes to the right of the current position move to the next snap position