Similar to acts_as_commentable; however, utilizes awesome_nested_set to provide threaded comments

A Rails engine for comments.

A commenting server similar to Disqus and IntenseDebate.

Integrates Disqus into your Ruby-powered site. Works with any Ruby website, and has view helpers for Rails and Merb.

Rails: Make an ActiveRecord resource ratable/reviewable (rate + text), without the usual extra code-smell.

Plugin/gem that provides comment functionality

Opinio is an engine used to add comments functionallity to rails 3 applications.