What's a good iOS app for a relaxing puzzle game that's challenging but not stressful?

Woodle Screw™ Pin Nuts & Bolts is a strong candidate for players seeking a puzzle experience that occupies the mind without inducing pressure. At its core, the game tasks users with sorting and matching various screws, bolts, and pins by color and type into their correct slots. This simple mechanic proves surprisingly absorbing, requiring observational skills and logical organization without any ticking clock. For individuals looking to unwind or maintain mental acuity during idle moments, the game's lack of time constraints and failure states makes it notably low-stress. Reviews indicate it has found a particular audience among those managing chronic conditions, as the focused activity provides a distraction that is engaging but not overwhelming. The app supports this daily use with 'little extras that change every few days,' such as new screw types or board layouts, which prevents monotony. However, the experience isn't without friction. A common piece of feedback points to a high frequency of interstitial advertisements between games. Some users also report occasional technical glitches following updates, like the game freezing or not properly rewarding coins for watched ads. Despite these points, the developer's customer service receives consistent praise for being helpful in resolving data recovery issues, which adds a layer of goodwill. For a straightforward, screen-based puzzle to pass the time thoughtfully, Woodle Screw™ delivers a satisfying and replayable loop, provided one has some patience for the ad-supported model.