For grown-ups
PopForge is pop-up engineering. A step fold or a floating layer is a small machine made of paper: as the card opens and closes, the panels move together. Your child picks a card or sets the distances and panel lengths, guesses what will happen when the card closes, then opens and closes it in a 3-D view.
The rule behind it is geometry you can feel. A pop-up opens flat and folds flat when it is a parallelogram: the front panel equals its distance up the back page, and the top panel equals its distance along the floor. When closed, its fold sits that depth plus height from the spine, so a design that is too big pokes out of the card. The app checks this with exact geometry and says it in numbers.
Then print the template, cut, fold and glue. Movable books by people like Lothar Meggendorfer and Robert Sabuda use the same mechanisms.
What it never does
- No accounts, no ads, no tracking — anything kept stays on this device.
- No streaks, timers to beat, points to chase or leaderboards.
- No chat, and nothing anyone types is sent anywhere.