Here’s how I invented the single modifier keypress that has found it’s way into some Apple products.
In 2006 I send a message to Alcor (Nicholas Jitkoff @ ) on the blacktree forum with the idea of a single modifier activation for Quicksilver.
My thinking was this…
You never use a modifier key(such as command or shift) by itself. It is always used with something. When you press a modifier key OS X is expecting you to press another key.
I was short of function keys. I had all my function keys assigned to something. I wanted a simpel way to activate Quicksilver with a single keypress.
So I proposed that Quicksilver be activated by the single press of a modifier key. (The command key).
I suggested that Alcor get Quicksilver look for how long you held the modify key down, and if you hold the modify key down for under 100 milliseconds, then Quicksilver treat that as invoking Quicksilver. Because, realistically, you never just press a modify key down briefly like that.
Alcor responded fast and within a week this functionality for ‘ Modifier-only activation’ was introduced into Quicksilver!
I am not aware of anyone else using modifier only activation…
In 2012 Apple introduced dictation into OS X and the had a feature to ‘press function key twice’ to activate dictation.
Take a look at the keyboard shortcuts for dictation in the current Apple OS X system preferences…
Granted, it’s not single modifier-only activation, but it’s close.
I don’t know if they borrowed this idea of me (via Quicksilver) or they came up with it themselves but I am happy to claim the credit!