Microsoft held a Windows 10 Press Event today. Among their many announcements today they talked about universal apps. Universal apps will allow the apps to run across a variety of platforms. The apps will be able to sync your information across a variety of devices.
Syncing will be done via their cloud platform, OneDrive. This will allow syncing of your data from apps such as Outlook, People, Photos, Calendar, and Music. For example Photos will cache your images directly onto OneDrive. It'll also be able to remove duplicates. The Music app will have the ability to upload your music collection to OneDrive.
Since Windows 10 Mobile shares the same code as Windows 10 for desktops, apps will be able to run on both devices. For example Microsoft's own Office suite will be identical across both devices. For the first time mobile devices will be able to run the exact same Office apps as desktops. The UI will just be modified for the smaller screens on mobile devices.