Smart-phone platforms: iPhone, Android, WebOS, Maemo, etc.
All are super-cool. But all are also astonishingly divergent in their approach to many of the details. So much so that one has to learn each one separately. My wife (an Android user) picks up my (webOS) phone and gets frustrated with it.
I find this particularly surprising since we’ve been making “intuitive” Graphical User Interfaces for a generation now, with standards that have been around nearly that long.
I’m sure they’ll converge again before too long, as (hopefully) the best ideas are adopted broadly.