I created an interesting new (free, web-based) puzzle app for mobile devices (works best on iPads, less-well-to-not-at-all on other devices). Want to try some challenging puzzles that blend spatial reasoning and manual dexterity? Just Slide to Unlock! https://slide.isohedral.ca/
@csk Maybe you can add a timer so that someone will speed-solve all levels. Like the Rubik's cube competition, we can have categories like two-hand, one-hand, blindfold, solve-with-feet.😂