Group count by creation date and sum of count-to-date.

group_and_count_to_date.sql

SELECT created_on, note_count, sum(note_count) OVER (ORDER BY created_on ASC)
FROM (
  SELECT date_trunc('day', created_at) AS created_on, count(1) AS note_count
  FROM notes
  GROUP BY created_on
  ORDER BY created_on DESC
) AS note_counting;
-- WHERE created_on >= '2013-01-01'