zenAud.io is designed for live use, so it currently doesn't have a piano roll -- instead, you define record loops using editing tools in the arrangement view and record MIDI or audio into it. You can also drag and drop to import standard MIDI files into the arrangement if you want to use pre-written stuff.
I realize this is a big limitation, but we intend to add a piano roll in the next few months.
I realize this is a big limitation, but we intend to add a piano roll in the next few months.