Scrible is an online tool that allows one to add layers of annotations to webpages, save them in the cloud and share them with others.
I had a quick go at it, it's maybe a bit fiddly to do some of the annotations but the app is definitely feature rich and with lots of potential uses, especially within an education scenario.
Here's how an annotation webpage would look like using the Google Chrome bookmarklet:
Various other tools for creating annotations are made available too:
Cite this blog post:
Industry Track, International Semantic Web Conference (ISWC-17), Vienna, Austria, Oct 2017.
Digital Humanities Quarterly, Jan 2017. Volume 11 Number 1
Digital Humanities 2013, University of Nebraska–Lincoln, Jul 2013.
Wittgenstein and the Philosophy of Information - Proceedings of the 30th International Ludwig Wittgenstein Symposium, Kirchberg, Austria, Aug 2007. pp. 319-335