Reading a book and seeing someone’s marginalia gives a whole new experience to reading the book.
Have a service that extracts your highlights and notes you make while reading ebooks. You can also input marginalia of real books you read. You then publish the feed to your marginalia and others can subscribe to it and see it on their ebook reader as they read the book. They can subscribe to marginalia from multiple people and see all of them while reading the book.
Infographics are fun and exciting, but they can also be a valuable teaching tool.
A website dedicated solely to infographics that teach you something. Allow anyone to publish these, and readers to subscribe to a daily dose of new ones in one or more areas of interest.
There may be an event happening or going to happen that will have many repercussions in many areas of which one or more are important for you. For example, you might be an EU member country citizen living and working in the UK, and Brexit might change the way you can stay in the UK. It would be good if you get the right information – and only the right information – for you about this subject.
Have an online center, where such events are covered but not generally. Instead only cover subjects that are each separately relevant to large groups of people. This way the person interested will get all the good information about what is interesting to him without having to go through a lot of information to find what he’s looking for. Have him subscribe to the event’s subject(s) that interest him and he’ll get a periodic email with all the new information and analysis that are of interest to him.