I recently showed someone how F8 lets you draw on the screen in Logos Bible Software.
See http://www.youtube.com/watch?v=G4XPnCbJbWo
And F7 brings up a quick text-comparison pop-over window when you use it in a Bible, or even while hovering over a Bible reference link.
These aren't easily discovered features, so I thought I'd mention them again for new users....
https://wiki.logos.com/Logos_Keyboard_Shortcuts_For_Mac
https://www.logos.com/ArticleViewer/2099 - Windows Shortcuts