Commentary:

• Double-click anywhere to comment.
• Comments are stored in simple text files.
• Comments for each file/URI are stored together in a single file.
• Edits to those files are reflected on the website (you do not have to use the web interface to manage the comments).
• Files are automatically committed to Subversion, if the comments are stored in a Subverion checkout.
• Comment locations are specified the id of an element and an offset. These are moderately resistent to getting lost as the document changes (though drifting is certainly possible). This is especially true for HTML generated with lots of ids; even better when the ids are meaningful (as in restructured text).
• Implemented as WSGI middleware, so it can be wrapped around any WSGI application. With an HTTP proxy WSGI application it could be wrapped around any website.
• Uses Javascript on the client side to make for a more pleasant experience