New filter for specifying the default author assigned to a post. Props tannerm
Bug fix: When filtering a user's published post count, use the value of their guest author profile if one is mapped.
Added support for checkboxes in Guest Author profiles
Fix Strict warnings from CPT's that don't define all capabilities
New swap-coauthors CLI command for replacing one co-author with another
3.0.5 (Feb. 18, 2013)
New filter 'coauthors_search_authors_get_terms_args' allows you to increase the number of matches returned with AJAX co-author selection
Bug fix: If there isn't an author term yet for a co-author, avoid an erronous join that caused duplicate posts to appear.
3.0.4 (Jan. 6, 2013)
Support for automatically adding co-authors to your feeds. Props cfg.
Bug fix: No Co-Authors Plus on attachments. For now.
Bug fix: Better support for co-authors with non-standard user_nicenames. Props STRML.
3.0.3 (Dec. 3, 2012)
Bug fix: The default order for the 'author' taxonomy should be 'term_order', in order for the author positions to stick. Props lgedeon
3.0.2 (Nov. 23, 2012)
Bug fix: Fall back to non-pretty permalinks when the author permastruct is empty, so that coauthors_posts_links() doesn't link to the homepage
3.0.1 (Nov. 21, 2012)
Add your own custom columns to the guest authors table using filters. Props cfg
A new wp-cli subcommand for renaming co-authors and another for removing author terms mistakenly assigned to revisions
Bug fix: Using a featured image for a guest author avatar didn't work. Now it does.
Bug fix: Don't assign author terms to revisions to avoid unnecessary database bloat
Bug fix: Make the coauthors_wp_list_authors() template tag work again
Bug fix: Improve capability filtering by properly handling super admin access and situations where user_id = 0
Minor UI enhancements for guest authors
3.0 (Nov. 12, 2012)
Create guest author profiles for bylines you'd like to assign without creating WordPress user accounts. Guest authors can have all of the same fields as normal users including display name, biography, and avatars.
Support for non-Latin characters in usernames and guest author names
wp-cli subcommands for creating, assigning, and reassigning co-authors
For themes using core template tags like the_author() or the_author_posts_link(), you enable Co-Authors Plus support with a simple filter
New author terms are now prefixed with 'cap-' to avoid collisions with global scope
Bug fix: Apply query filters to only post_types registered with the taxonomy. Props Tom Ransom
Filter coauthors_posts_link_single() with 'coauthors_posts_link'. Also adds rel="author". Props Amit Sannad and Gabriel Koen
Filter for the context and priorities of the Co-Authors meta boxes. Props Tomáš Kapler
Renamed the post meta box for selecting authors so it applies to many post types. Props John Blackbourn
2.6.4 (May 7, 2012)
Bug fix: Properly filter the user query so users can AJAX search against the display name field again
If https is used for the admin, also use the secure Gravatar URL. Props rmcfrazier
2.6.3 (Apr. 30, 2012)
AJAX user search is back to searching against user login, display name, email address and user ID. The method introduced in v2.6.2 didn't scale well
French translation courtesy of Sylvain Bérubé
Spanish translation courtesy of Alejandro Arcos
Bug fix: Resolved incorrect caps check against user editing an already published post. See forum thread
2.6.2 (Mar. 6, 2012)
AJAX user search matches against first name, last name, and nickname fields too, in addition to display name, user login, and email address
Comment moderation and approved notifications are properly sent to all co-authors with the correct caps
Filter required capability for user to be returned in an AJAX search with 'coauthors_edit_author_cap'
Filter out administrators and other non-authors from AJAX search with 'coauthors_edit_ignored_authors'
Automatically adds co-authors to Edit Flow's story budget and calendar views
Bug fix: Don't set post_author value to current user when quick editing a post. This doesn't appear in the UI anywhere, but adds the post to the current user's list of posts
Bug fix: Properly cc other co-authors on new comment email notifications
Bug fix: If a user has already been added as an author to a post, don't show them in the AJAX search again
Bug fix: Allow output constants to be defined in a theme's functions.php file and include filters you can use instead
2.6.1 (Dec. 30, 2011)
Fix mangled usernames because of sanitize_key http://wordpress.org/support/topic/plugin-co-authors-plus-26-not-working-with-wp-33
2.6 (Dec. 22, 2011)
Sortable authors: Drag and drop the order of the authors as you'd like them to appear (props kingkool68)
Search for authors by display name (instead of nicename which was essentially the same as user_login)
Option to remove the first author when there are two or more so it's less confusing
Bumped requirements to WordPress 3.1
Bug fix: Update the published post count for each user more reliably
2.5.3 (Aug. 14, 2011)
Bug fix: Removed extra comma when only two authors were listed. If you used the COAUTHORS_DEFAULT_BETWEEN_LAST constant, double-check what you have
2.5.2 (Apr. 23, 2011)
Bug: Couldn't query terms and authors at the same time (props nbaxley)
Bug: Authors with empty fields (e.g. first name) were displaying blank in some cases
Bug: authors with spaces in usernames not getting saved (props MLmsw, Ruben S. and others!)
Bug: revisions getting wrong user attached (props cliquenoir!)
2.5.1 (Mar. 26, 2011)
Fix with author post count (throwing errors)
2.5 (Mar. 26, 2011)
Custom Post Type Support
Compatibility with WP 3.0 and 3.1
Lots and lots and lots of bug fixes
Thanks to everyone who submitted bugs, fixes, and suggestions! And for your patience!
2.1.1 (Oct. 16, 2009)
Fix for coauthors not being added if their username is different from display name
Fixes to readme.txt (fixes for textual and punctuation errors, language clarification, minor formatting changes) courtesy of Waldo Jaquith