Braincup is great!
https://f-droid.org/packages/com.inspiredandroid.braincup
Train your brain with fun mini games that challenge your memory, focus, logic and math skills. Braincup offers 15 brain training exercises designed to sharpen your mind and improve concentration.




















F-droid themselves gave an update in April:
https://f-droid.org/en/2026/04/03/twif.html
So it seems since the handover things have settled but there is also a new fork which takes a more bare-bones approach.