Why web pages annotation tools are not killer applications? A new approach to an old problem

The annotation of web pages, and the possibility to share the notes with others, seems to be a powerful tool. Although several tools already provide such possibility, they are not as widely popular as one would expect them to be. We try to explain this fact, and propose a novel architectural approach that is, in our view, particularly suited to some particular domain such as e-learning. We also present a tool that implements the proposed architecture.