In the real world, people add their own layer of information on top of printed documents by scribbling notes on them, and highlighting passages. They can share the modified document with their friends, and pass on their opinions and insights.
This is really hard to do on the computer. Distribution formats like HTML pages and pdfs are designed to deliver information from the producer to the consumer. You can’t even add your own notes, let alone share them with others.
With the real-world analogy so glaring, there’s been a lot of attempts to fix this. The wikipedia article on web annotation alone includes twenty-two active projects! In a different direction, MS Office now includes OneNote, which is a tool for creating free-form notes, and sharing them with friends. It focuses on pulling content into a separate notebook, rather than adding notes on top of the content.
So why haven’t you heard of most of these web annotation tools? Casey has a post covering the history of web annotation, from 2004. There’s been a few successes since then, but most of the annotators have struggled to get the critical mass of users they need to be useful. One of my favorites is JumpKnowledge, which has a focus on letting you email pages with your comments on top, using their AWE Firefox plugin.
Reading their blog is pretty painful. When Yaakov describes trying to get coverage for their system as "like banging my head against a wall" I can sympathize. He’s got some great reviews, from some big names, but it seems like even they’re no longer in active development.
[Update- I just heard from Yaakov, and they have been working on some interesting new features, which is great news! See his comment on this post]
This is a good reminder you can build it, and they won’t come, unless you get marketing and distribution right too.
Diigo seems like the most successful annotator out there at the moment. It’s in active development, supports a lot of cool features like sharing with groups, and some neat search functionality for things like looking for inbound links to the current page, or searching on the same site. Trailfire is another very active annotation tool, that does some content analysis of the page you’re on to figure out if there are related pages in its database.
It still feels like the killer app for web annotation is missing. Maybe people really don’t want to scribble on web pages as much as us techies think, or maybe we just haven’t found the right way to do it. I thought that JumpKnowledge‘s focus on mailing web pages together with annotations had a lot of potential, but it doesn’t seem to have caught on. Diigo has tools for easily posting annotated pages to a blog, which also seems like it could be really popular, but I don’t see too many blogs being created that way.