Most of (maybe all, can someone confirm) Andrew Braybrook's games used the HELP key as the pause function, and ESC while paused would quit.
Rainbow Islands, Fire & Ice, Uridium 2, Virocop, etc.
Also, using Amiga applications, if on-line help is available then HELP is the key to see it. A feature I miss when using more modern OS's. To me it makes more sense to have the HELP key far away from the function keys.
It's a pain in the arse when one accidentally hits F1 (when aiming for ESC of F2) in a Windows app, when one has to wait five minutes for the on-line help window to appear before one can continue (MS Word anyone?).