The Quantum Quest

Cool they made a custom edition of a quantum circuit simulator that introduces concepts one by one. It's based on this general purpose QC simulator https://github.com/Strilanc/Quirk#examples (check the animated gif demo; very powerful stuff)

Lol... with V8 and SpiderMonkey getting faster and faster, quantum computing simulations in js are probably as powerful as anything that can be done in a lab these days ;)