uChecker is a menu-bar Mac app that proofreads and rephrases your text right on your device. Hit a global hotkey, or use it from the Services menu on any selected text, and get corrected text back in one click. Proofread also shows exactly what changed, tagged by type. On-device by default: no account, no tracking, no cloud unless you opt into your own custom endpoint. Runs on Intel Macs too, via free offline spell-check. Free on the Mac App Store.
