Crossword Replay lets you solve crosswords and then replay the puzzle, at whatever speed you choose, square-by-square, so you can see where you went wrong and then (hopefully) recovered. Its fun, its free, and it works with any crosswords in a .puz format. Crossword fans have been clamoring for this capability for years, and now its here!
Version 2.0 now includes the ability to save playback files (shared via iCloud Drive, so get to them from anywhere); the ability to control playback speed, and pause during playback to contemplate a particularly thorny point; calculate statistics, including median solve times (much better than the average); make a note of your favorite clues so you can study them at your leisure.
All this for a low, low price of $0