Convert is a good unit converter. I don't know if it's free: my father gave me his old phone and it was already on there.

PicGrid is an addictive hanjie game. The lite version is free.

WordTrail is a Boggle-style game. The aim is to unscramble a nine-letter word. The only problem is that some of the words are things no reasonable person could be expected to guess. Another one I inherited from my father.