I was in a meeting today of The Open University's accessibility practitioner's group. Louise Olney, a project manager in Learning and Teaching Solutions kindly came to talk to us about OU Annotate, and in particular the work that is being done to improve it's accessibility.
"OU Annotate enables you add your own annotations to web pages. You can create an annotation for an entire web page, like a bookmark, or you can select and highlight specific text. You can add comments and tags to your annotations and, if you wish, share them with others."