At least 33 hackathon projects were developed and showcased in 3 days, all crowd-documented at https://phabricator.wikimedia.org/T96378 before the end of the event. Unseen in Wikimedia as far as I'm aware, and we'll try again in Wikimania
For instance, Experiment with video.js was basically a one-person-three-day effort (but not just any person, TheDJ no less), and it was demoed with a functional and funny sneak preview. https://phabricator.wikimedia.org/T100106