Bimaru is a fun puzzle. I remember putting an Android App in the store containing the phrase "Battleships", only to receive a copyright claim from Hasbro, and Google immediately took the App down from the Store.
I also mostly enjoy Sudoku variants, most of which I discovered via Geocaches, interestingly.
After solving a few I then implemented a solver with customizable constraints, if anyone's interested, should still be available here:
My personal blog, mostly coding/tech and GameBoy related posts, usually about one post per month