Next! Fitness - A.I. powered gym
Brain Games - Boost memory power with free brain games
Focusmate - Distraction-free productivity via virtual coworking
Dualnback.works - Dual N-back is a specific brain training exercise, that's been shown by research - it might improve fluid intelligence.
BodyGuide - The app that helps you self-solve aches, pain and tension
Pixelogic - Daily Picross - Nonogram logic game with 5000+ puzzles and a daily puzzle