Pull more records based on IDs in comma separated list returned by GROUP_CONCAT
I think you could use the following query to get the data you need:

SELECT 
  users.username,
  title, content
FROM articles 
LEFT JOIN users ON articles.author_id = users.id
GROUP BY articles.author_id , title
ORDER BY  articles.author_id ,articles.published DESC;


The presentation of it depends on the programming language you will use to display the results.