Apple Sharpener is a macOS system tweak that programmatically removes or customizes window corner radii, producing sharp (square) corners on application windows and optionally modifying the Dock's corner radius. It operates as an injectable dynamic library (dylib) loaded via the Ammonia injection framework and provides a CLI tool (`sharpener`) for runtime control. The architecture is a classic method swizzling tweak: the dylib hooks into `NSWindow` methods (`setFrame:display:`, `_setCornerRadius:`, `_updateCornerMask`) and the Dock's `CALayer` (`layoutSublayers`) to enforce a configurable corner radius. State is persisted via `NSUserDefaults` (in a shared suite) and communicated between processes using `notifyd` distributed notifications, allowing live changes without restarting applications. The tweak intelligently filters windows to affect only standard titled windows (excluding HUD, utility, popups, and small UI elements) and handles fullscreen mode gracefully. This is a targeted utility built for a specific use case within the macOS jailbreak/tweak ecosystem, demonstrating solid Objective-C craftsmanship and careful integration with the Cocoa framework.