Keyameleon

Keyameleon is a free, open-source macOS menu bar app that gives every physical keyboard its own input source. Plug in your external Italian, German, UK or JIS keyboard and Keyameleon switches to that layout the moment you start typing on it, while your MacBook's built-in keyboard stays on US. No shortcuts to remember and no manual switching in the menu bar.

Under the hood it watches which keyboard each keystroke comes from using Apple's CoreHID in listen-only mode, switches the input source, and verifies that the switch actually happened. It never modifies or injects keystrokes, and it collects no telemetry. Keyameleon is signed and notarized, updates through Sparkle with your approval, installs as a DMG or via Homebrew, and is MIT licensed. Requires macOS 26 or later.

• A dedicated input source for each physical keyboard
• Automatic switching the moment you type, with verification
• Never modifies or injects keystrokes; no telemetry
• Lives in the menu bar, with guided setup
• Signed and notarized, Sparkle auto-updates
• Free and open source (MIT), DMG or Homebrew