Karabiner Elements (earlier was Karabiner, and even earlier was KeyRemap4MacBook) is powerful and stable keyboard customizer for macOS.

Features:

• Simple Modifications: Map normal keys to arbitrary key functions
• Complex Modifications: Map keys by complex rules. e.g., key to modifiers, modifiers+key to key, send key event if pressed alone, etc
• Function Keys: Map function keys to arbitrary key functions
• Devices: Apply modifications to specified keyboards only
• Profiles: Support the creation of multiple profiles that the user can switch between
• Modifier Flag Sync:Synchronize modifier flags across all connected keyboards
• Secure Keyboard Entry Support:Work well on Secure Keyboard Entry environment such as a password prompt, terminal with Secure Keyboard Entry, etc