HeapViz is my most ambitious side project. It's a tool for visualizing Chrome memory profiles, with the goal of easily identifying memory leaks. It was a tour around advanced web technologies, including WebAssembly, WebGL, and web workers.
Heap profiles can have millions of nodes, so non-blocking performance was critical. Making those millions of nodes interactive is also challenging as you can't just attach click handlers to the DOM, you need a more refined approach.