Generally I found GNUstep is currently incompatible also among different operating systems/environments, which makes the usage of keyCodes under GNUstep impossible.

I see this is a moot topic here. I did consult only the Apple documentation and was a bit confused by things now working properly afterwards.

An added point is here probably that "esc" cannot be handled by characters and it is not present among the unicode constants, which I find very strange (check the second link posted by Matt)

Currently I worked around this by defining myself a constant and assigning it different values between gnustep and mac. I hope that GNUstep returns the same code on different pplatforms.

Secondly, I agree that "hardware independent " is also misleading here: it means only that the same os run on different hardware will return the same code, it does not speak of different implementations. But, of course, since OpenStep is no more, APple does not consider Cocoa itself portable, so it ends up just meaning that different apple computers and keyboards will return the same key code. Our scenario is slightly more varied!

We can close this bug if we think there is no good solution, but it will remain of course a point where a potential user porting his mac app might remain confused, maybe we a wiki entry?

I'm not entirely sure this is a bug ... saying that the codes are device independent is not the same as saying they are system independent, and I can't actually find any definition of what the key codes should be (except for function keys ... and we probably already use those definitions) in the documentation or Apple's AppKit headers.

Please could you provide a link to a definition of what those keycode values are?