PC Outline (PCO) was very good in its day. I was using it under DOS in 1985 and some people are still using it today in a Windows DOS box.  It gave me the opportunity to move over from a long-form prose approach to &#x27;writing things down&#x27; to something far more concise and well-structured.  Nowadays the Outliner functionality space is very full of product but it seems that PCO itself led nowhere.