puRRing - Cute cat videos with every incoming call on your Android
Brain Games - Boost memory power with free brain games
Cleartones - Minimalist ringtones
Dualnback.works - Dual N-back is a specific brain training exercise, that's been shown by research - it might improve fluid intelligence.
LibreContacts - Add WhatsApp profile photos to your phone contacts.
LeveLisa - The brain game that creates creativity