I recently got another long-running collaboration to the point of having something to show — a first-person shooter in the browser. This was an idea which Sally, my youngest, had. She drew a bunch of house fronts, and also some ‘zombies’, and then a map of the world where the action takes place. The result is hosted on GitHub pages:
It requires a WebGL-capable browser, and I have not put effort into graceful behaviour if this requirement isn’t met. There are some more details, and also the repo itself, on GitHub, although it’s just a dump of the final state of the work rather than a useful history.