Keynote presentation in conjunction with other app?
You can use the H keyboard shortcut while the presentation is running. This (according to the help displayed using the ? shortcut) is used to "Hide the presentation and switch to last application used".
If you make sure the application you are wanting to demo is the last application used, you can do the following
- Go through your presentation until you get to the Demo slide
- Press H to switch to your application
- Demo the application
- Use ⌘ + Tab to switch back to Keynote
- Your presentation resumes from the Demo slide.
Using H to hide Keynote works fine to reveal an app that is not full screen.
To switch from Keynote to a full screen app you must go to Keynote preferences and in the "Slideshow" section of the preference window check "Allow Mission Control, Dashboard and others to use the screen".
Now you can switch from a running presentation to another full screen app using a three finger swipe (at least by default). This works with one or two dual screens.
However to switch back to the running presentation you need to use ⌘ + Tab. You cannot use a three finger swipe!
This is the only way I've gotten it to work anyway! (Yosemite 10.10.5 or El Capitan 10.11.1 with Keynote 6.6.1)