Developers can finally start getting their hands dirty with making Windows 10 (mobile) specific apps, as the documentation for the Windows 10 specific controls are finally documented on MSDN.
The documentation includes controls for the CalendarView, CalendarPicker, SplitView, RelativePanel and Searchbox.
At present only the RelativePanel works on Windows 10 Mobile Technical Preview, but of course eventually all the APIs will be present on both versions of the operating system.
The documentation can be seen at the links above. Thomas Nigro, the developer of VLC for Windows Phone, has explored some of the APIs in a blog post here.