A zombie survival game that was made by a funky guy called Nelson Sexton.
Unturned is a blocky game with guns. It is currently quite popular gaining over 20,000 players at once.
Previous Unturned versions was viewed by large youtubers like Pewdiepie and Jacksepticeye.
Literally, it means you have turned over and looked beneath every possible stone. Idiomatically, it means you've looked everywhere you could and have done everything you could to try to solve some problem.
Dev: Didn't you find my book yet?
Ted: Believe me, I've left no stone unturned and did't find it.