Brain Games - Boost memory power with free brain games
Hellosaurus - Interactive mobile shows kids can play, not just watch
Dualnback.works - Dual N-back is a specific brain training exercise, that's been shown by research - it might improve fluid intelligence.
Tellast - Write stories collaboratively with others
Pixelogic - Daily Picross - Nonogram logic game with 5000+ puzzles and a daily puzzle
Hullabalu - Interactive stories for kids