" the education startup Highlighter has been tackling, initially offering a JavaScript plug-in enabling "comments in the margins" on blogs and websites. (I chose Highlighter as one of my favorite startups of 2011). Since then, the startup has shifted its focus slightly to become an education publishing platform that lets textbooks be published for the Web (as well as in PDF, Word, PowerPoint, Excel and ePUB) - all with built-in social marginalia features."