Cotypist sits in the macOS menu bar and surfaces word-completion suggestions as you type, accepted with a Tab keystroke, across whichever apps you have open. The differentiating mechanic is per-app instruction profiles: you teach it one voice for client emails, a different register for pull-request descriptions, and it holds those rules separately per application. On-device processing keeps your keystrokes off external servers. The free tier caps daily output at 100 words — a ceiling that arrives fast for anyone with real writing volume. No API, no Windows build, no self-hosting path exists.