In case you never came across any ‘Web Annotation’ service before, than basically what it is, is a bookmarking tool (usually in the form of browser addon or bookmarklet) that allows users to annotate (add sticky notes, highlights, etc.) any desired webpage and store it online.
There are many cool things you can do with them, i.e. (1) quickly add sticky-like memos to your bookmarks, (2) bookmark long articles with relevant text being highlighted, (3) store, organize and tag annotated pages online and most importantly (4) share your annotations with friends or project/assignment group members.
(1) Diigo

Features: (Demo)
- Add notes and in-page highlights
- Store, Tag (categorize) and Share webpages (via email, RSS, blog, group, etc.) along with your notes and highlights
- Create groups (i.e. private group for team members)
- Subscribe to specific webpages’ notes (i.e. to all notes tagged as ‘funny’)
- Right-click menu option to search for highlighted terms (on websites, on major search-engines, social bookmarking systems, blogs, etc.)
- Supported browsers: IE, Firefox and Flock
- suitable for collaboration
(2) Stickis

Features: (Demo)
- Add notes
- Save, Share and Tag (categorize) your notes
- View, save and comment on webpage’s notes by other users from any webpage
- Subscribe to notes by others (by tag, by webpage, by user)
- Create groups
- Supported browsers: IE and Firefox
- suitable for collaboration
(3) SharedCopy

Features: (Demo)
- Add notes, in-page highlights, draw lines, circles and squares
- Store annotated webpages and Share them with others via URL
- follow-up on changes made to specific pages via RSS
- Integration with Twitter and BaseCamp
- Supported browsers: All
- suitable for collaboration
(4) Fleck

Features: (Demo)
- Add notes
- Publish annotated pages on your blog
- Share annotated webages with friends (via URL)
- notes can be edited and saved by anyone knowing it’s location
- Supported browsers: IE, Firefox + Bookmarklets
(5) MyStickies

Features:
- Add notes
- Store, Tag and Search annotations
- Supported browsers: Firefox
(6) JKN

Features: (Demo)
- Add notes to one or multiple pages
- Add numbered points between words
- Comment on and print annotated webpages
- Share annotated webpages via URL, email or blog
- Supported browsers: IE and Firefox
(7) TrailFire

Features: (Demo)
- Add notes (aka trail marks) and save annotated webpages
- Categorize annotated webpages (assign them to Trails)
- Invite others to view and collaborate (wiki-style) on your trails
- Subscribe to desired Trails
- Supported browsers: IE and Firefox
(8) DrawHere

Features:
- Add notes, highlights and drawings
- Save, Tag and Search your annotations
- Share annotated webpages (via email or embed in your blog)
- Supported browsers: All
(9) ShiftSpace

Features: (Demo)
- Add notes, highlights, add/change images and text
- Save and Share annotated/edited pages via RSS
- Supported browsers: Firefox (requires Greasemonkey)
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Have you checked out Protonotes (http://www.protonotes.com) ? Only has the basic annotation features, but by far the easiest to use.
@Sarah
Tahnks. Loooks good, I’ll mention it in one of the upcoming ‘extra’ posts
[...] Top Web Annotation Tools: Annotate+Bookmark+Collaborate [...]
[...] Full Article: Top Web Annotation Tools: Annotate+Bookmark+Collaborate [...]
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I’ve tried all these services/apps and, as usual, find that what I really need is a way to mash them up. Each has features I like, but all lack at least one essential feature that others have.
Diigo has the best feature set for me. You can highlight text (or anything) on a page, and make a stickynote associated with that highlight. The note isn’t visible to readers until they place the cursor on the highlight, then a window pops up with the note in it. This means that the flow of the article isn’t interrupted by inline notes, and none of the text is obscured. Once you’re done highlighting, you can save and email the url of the highlighted page to anybody. By clicking on the link in the email, the recipient is taken to the marked-up page and can read the notes by running the cursor over the highlights. All this is great except that it doesn’t work with dynamically-generated pages, which more and more pages are.
Fleck is my second favorite. It seems simpler and less buggy than Diigo, and it hides comments in in numbered footnote markers. Clicking on the marker opens it and lets you read the note. Unfortunately, Fleck doesn’t support highlighting, so one has to guess exactly what the note refers to. I use annotation for editorial markup, so I want to, for example, comment on a phrase inside a sentence. With Fleck, the reader can’t be certain just which words are involved. And, as far as I know, dynamic pages don’t work here, either.
SharedCopy does allow highlighting and should work with dynamic pages but, while it does allow you to reduce the size of the note somewhat, the text box is still big enough to obscure part of the text, especially if the comment is a long one. This could maybe be overcome by the fact that it lets you draw lines, so you could draw a line from the highlighted portion to a text box tucked somewhere out of the way. Problem is, the line is so faint as to be almost invisible, so that really doesn’t work, either. This would be an excellent choice for me if they would only make the text box reduce to a point, as in Fleck, or only pop up when the highlight is selected, as in Diigo.
JumpKnowledge highlights your comments and puts them inline, like Google Docs. They think this is a virtue because none of the text is obscured, but I find that an editorial comment inserted into the middle of a sentence totally disrupts reading. Again, it works with dynamic pages, and would be great if only one of the previously mentioned techniques for hiding notes was employed.
Stickis and Mystickis both just place stickynotes wherever you want them, and don’t offer the precision I need. TrailFire is almost in a different category from all the others, allowing, as I understand it, only one comment per page, so not really for making detailed comments on portions of pages. Draw Here is available only to other members, so you can’t email pages, and your markups can be overwritten. ShiftSpace is a horse of a different color, too. I’m not sure I really understand it, but it looks like a given website can be annotated only if it has ShiftSpace on the server. It has some cool features, like the (experimental) ability to swap site content, but seems to require a higher a higher level of geekism than I can manage.
Other people want to use these applications in very different ways than I do, so I’m not suggesting I don’t like wouldn’t be good for somebody else. They’re all pretty nifty, actually.
Another one to try is A.nnotate.com - it lets you annotate uploaded PDF and Word documents (sample) as well as snapshots of web pages. Highlight text to create a note, notes can be shown as draggable boxes, in the right margin or as footnotes. Notes and highlighted terms are used to build up a searchable index, with page previews, and each note can also have replies and tags for workflow / reviews. The focus is on discussing and indexing documents and web pages online with colleagues.