One built-in way is to use Automator to create a Service, and then bind F19 to that service. One wrinkle is that you (apparently) cannot assign a function key directly to a service using the standard UI; but you can create an Application Shortcut to invoke the service by name.
First, create the Service with Automator.
- Start Automator. If you don't know where it is, use Spotlight.
- When prompted for a template for the new workflow, choose Service.
- At the top of the service workflow, is "Service receives selected" -- choose "No input" at the bottom.
- The Library should be visible on the left. If not, click Show Library in the toolbar.
- In the Library, search for "launch". "Launch Application" should appear.
- Drag it to the workflow.
- Choose Calculator in the popup for the action.
- Save this workflow with a name like "Launch Calculator"
The Service is saved in your home directory, in ~/Library/Services (where you can delete it if you later decide you don't want it). Now create the key binding.
- Under the Automator menu (actually almost any app), where Quit is, highlight
- In the menu to the right,
Launch Calculator should already be listed as a "General" service. But it has no key assigned to it.
Services Preferences... under it. This opens System Preferences, to the Keyboard Shortcuts page of the Keyboard panel.
- "Services" should be selected on the left.
- If you scroll all the way to the end on the right, you should see "Launch Calculator" under "General"
- You can double-click the blank area on the right end of the item -- where the keyboard shortcut is listed for the other ones that have something bound -- and when the text box appears, hold down a new key combo. But this does not work for function keys; it doesn't "take", and the text box doesn't go away, as it does with some other combo, like
Ctrl-Option-Command-Asterisk -- at least not for me.
- So Click the
+ under the list box (to the left of "Restore Defaults") to create a new Application Shortcut
- Application: "All Applications". Menu Title: "Launch Calculator". Keyboard Shortcut:
Now switch to any other app and look at the Services menu.
F19 should be bound, and so it will work with almost every app. (Two tidbits: it's not bound inside the System Preferences app the moment you create it, so you can't try it immediately; you have to switch away and come back for the menu to get updated. Second, the Calculator app does not have a Services menu, so you can't launch Calculator from Calculator, although the Launch Application action should handle that in theory, doing nothing since it is already active.)