[GuiA]

Yes- I always point to f.lux as an example of little feature that every single graphical operating system could benefit from having, and yet that no OS creator includes as a feature. More than that- I want an entire OS that has dark on light windows/text/widgets/etc. during the day, and light on dark at night - this would be configurable, but by default automagically determined by your geographical location. On OSX, one can hack such a setup using an app like Nocturne, but it's clunky.

At every new Windows, OSX, iOS, Android release we get new features (some debatably useful - i.e. notification center in OSX, or integration with the new social network of the day) - but some key stuff that would make human-computer interaction noticeably better is just missing.

A few other things that I can't believe are still not standard in a 2014 OS: better copy and paste (the damn thing has been clunky for 30 years, see Ted Nelson's rant), better window management, better support for interacting across multiple nearby computers (Airdrop is a tiny step in that direction), ...