Co-author plus: list of posts by authors in the sidebar

Not sure if you’re looking for an “automated” way of doing this, but in code you can get an array of all co-authors by using $authors = get_coauthors();. Once you have your authors array, you can loop through it and use each author object’s ID to get posts by that author:

$authors = get_coauthors();
foreach ( $authors as $author ) {
    $args = array( 'author' => $author->ID );
    $posts = get_posts( $args );
    // echo out your posts
}