Windows: use Alt codes with the numeric keypad
Windows: use the US-International keyboard layout
Windows: use the Character Map app
Mac: press and hold a letter key to see accent options
Mac: use Option/Alt key combinations
Mac: use the Keyboard Viewer
iPhone/iPad: press and hold a letter key
Android: press and hold a letter key
Linux: use Compose key combinations
Linux: use Unicode input with Ctrl+Shift+U
Copy and paste accented characters from a character map or online source