Sudoku on a 16x16 grid. The ones I’ve found so far I didn’t like because they didn’t have any way to highlight candidate numbers, which is indispensable when sifting through so many possibilities.
ETA: playable on PC that is, not downloaded puzzle pages.
Bump. There are lots of hexadecimal Sudoku, but I haven’t found one I like yet.
Conceptis Puzzles (conceptispuzzles.com) sometimes has 16x16 puzzles with the numbers 1-16, not the hexadecimal numerals 0-F.
They have free weekly puzzles, but the free ones are usually the easier ones, and I have not played a 16x16 puzzles that I didn’t have to pay for, though. Since I generally save my points for buying the puzzles that I most enjoy, which does not include Sudoku, I do not know for sure that they have a new 16x16 puzzle each week.