Folder for puzzles attempted but not solved.
So you can find them again! Best would be a folder for all puzzles purchased with points (from community-made puzzles using the feed, featured, and most-played lists, and the search feature), whether solved or not. Sometimes you have to exit the app before you have finished a puzzle; the app then opens to the home screen and there is no way to easily find the puzzle again.
This is now available on Android, and will be released in the next week or two on iOS.
Yes!!! This. Please!!!