Reaper is a powerful digital audio workstation (DAW) that allows for the playback of piano rolls. To show piano rolls in Reaper, you first need to select the track you want to view and then go to View > Piano Roll from the main menu. This will open up a window where you can view and edit your MIDI notes. You can adjust velocity, note length, pitch bend, vibrato and other aspects of each note with ease. If you have multiple tracks selected at once, all their respective piano rolls will be shown in an array within the same window so that they are easier to manage together.