Sift.pics is a spin-off of Ajapaik.ee for crowdsourcing basic categorisations to historic photographs. Users have to make binary categorisations (currently out of 7 pairs of decisions) whether a picture is interior or exterior, has one person or many people on it, etc.
The code hosted here is a Django application implementing the tagging and also sorting functionality for the albums added to Sift.pics. The app also serves Sift.pics android app via Django REST Framework. The mobile app only has the tagging functionality (no sorting interface).
Our (official) instance: https://sift.pics/ Sift.pics at Google Play Store: https://play.google.com/store/apps/details?id=pics.sift.app