I have TacticMaster (available on F-droid) but your app looks more polished and will have to give it a try as well.
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I'm the developer of rdx, a mildly popular ad-free, privacy and user friendly Reddit client. This time, I made something for a very specific use case: solving chess puzzles with no internet.
Why? Well, my Wi-Fi is terrible in the bathroom—and that's where I do some of my best thinking. I tried printing out “mate in X” puzzles to solve offline, but they weren’t fun without interaction. So I built OffChess.
OffChess is an iPhone/Android app that contains over 100,000 chess puzzles, fully offline and completely ad-free. You can solve puzzles by category (Mate in 1/2/3/4/5, tactics like pins/forks/skewers, or openings like Sicilian/French, etc). You gain or lose points based on how you perform, so there's a light rating system to keep things engaging.
No accounts, no tracking, no monthly subscriptions, no internet required. Just pure, old-school tactical chess training, wherever you are.
You can check out the iPhone/iPad app at https://apps.apple.com/us/app/chess-puzzles-offchess/id67447... or the Android app at https://play.google.com/store/apps/details?id=com.offchess
Would love feedback, bug reports, or suggestions.
Thanks!