Com_comments is a project mainly written in ..., it's free.
Nooku Framework Comments Component
/**
@license http://www.gnu.org/copyleft/gpl.html GNU/GPLv2 */
This component can be used to enable users to add comments to any item you like.
INSTALLATION
Simply download the package and symlink from the Joomla installation
/components: ln -s com_comments_directory/site com_blog /language/en-GB: ln -s com_comments_directory/language/en-GB.com_comments.ini en-GB.com_comments.ini
USAGE
Add a com_comments entry to the jos_components table and create the DB tables found in sql/
You can add comments to any Nooku component simply putting a line of code in your view tmpl file.
For example, this line puts in the page all the comments (and the comment entry form) referring to the post 1.
<? KFactory::tmp('site::com.comments.controller.comment') ->sort('comments_comment_id') ->direction('asc') ->target_type('post') ->target_id(1) ->return(KRequest::url().'#comments') ->limit(0) ->browse(); ?>
Tested on Nooku Framework rev. 2513