It is installed by simply inserting the library into the web pages and defining few settings. The annotations can either be stored in a free service called AnnotateIt or locally.
In order to annotate a string, just select it, click the appeared "edit" icon and there you have the options. You can choose the annotation to be viewable and/or editable by others.
The annotations can have comments, tags, users and more (it can be extended easily).
Annotator is handy for teams that are working on the same project and where everyone has a word to say : ).
Compatibility: All Major Browsers