One of the coolest things I made was my final year project at uni - a real-time testing system for primary schools with Node.js, Socket.IO, Express & MongoDB. Teachers could create, save, share and schedule tests, during which they could monitor any chosen pupil's test in real-time - watching what they clicked on, which question they were on, what questions they'd answered correctly (and incorrectly) etc. It marked and graded tests, created graphs of results and lots of other cool stuff too.
An EPiServer project with a pretty complex front end Bootstrap based system for which I did the majority of front end work.
The websites / apps / games / tools / demos on this page are only a drop in the ocean of the projects I've worked on. I really need to start blogging about some of the new stuff!