For this, for sure have a look at WebVOWL. The authors have done a lot of research regarding the visualisation of ontologies. Really nice stuff.
@tuelsch I noticed that whattheontology uses rdflib.js. A little while ago I looked into adding a d3 serializer to rdflib.js so that graphs can be visualized with it. Unfortunately I have been distracted and have not completed that work. D3 is also used by Webvowl . They use a D3 force simulation, which I think would be not too hard to add to rdflib.js. The changes I think can be pretty much localized to two files: serialize.js and serializer.js. This will I think be ok for smaller ontologies, but I think for larger ones 3d will be necessary to make sense of them and then also some kind of paging will be necessary. I would suggest not going too far with the visualization in the first iteration. For one thing its a very big subject, and for another thing the rdf library space also has comunica which probably eventually will have some fancy visualization features.
An app along the lines of Quizlet but better, where quizzes, their answers, study sets and flash cards could be composed and others could take quizzes, with their answers, scores, achievements and qualifications being stored on their pods.
Spam detector for your inbox. The same as for your email inbox, but for the inbox of your POD. Fully customizable with rules.