Good question. When I was briefed by Microsoft about Windows 10 on ARM my jaw dropped. We heard rumors they were working on it, but no one was expecting that announcement at WinHEC. It's a huuuuge deal that many people have not recognized yet, but will.
Windows Holographic being built into Windows 10 and Composable Shells are also huge.
For Mobile I guess it was the Skype/SMS thing. Continuum is up there but that came out in late 2015 technically.