Microsoft announced at Ignite, a single mobile app for its entire office suite. Including Outlook. All up, it’ll save some screen space.
Note that there are some limitations. This is likely to change so remember, search is your friend.
This now gets a little confusing. There is also a free version of Office for Windows devices with screens less than 10″. As of time of writing, its still available. Whether it gets updates is possibly another story. Even with the Surface Go still being around.
But certainly it continues Microsoft’s focus less of operating systems and more on services.