The copy-editor of the web
Annotations can have comments, tags, users and more. Morever, the Annotator is designed for easy extensibility so its a cinch to add a new feature or behaviour.
Adding annotation to your webpage using the Annotator is easy. Full instructions are in the Getting Started section of the docs, but it is just two short steps. First, you need to download the Annotator library (or link to the hosted version), include it on your page along with jQuery. Then add the following line to initialize the annotator.
You'll need to store your data somewhere, luckily we've made this very simple to do using AnnotateIt, a hosted web service for storing annotations.
Alternatively if you'd like to integrate the annotator with your own storage system check out the Docs for more information on the annotation format and store plugin.
The bookmarklet is a simple tool that allows you to add the annotator to any webpage and save your annotations to AnnotateIt. Check it out at http://annotateit.org/.