For the quick preview of all screens, you can use this link:
https://sunnyswan296822.invisionapp.com/console/share/G6EYDAQZ5F3

Best viewed on a PC, use arrow keys to navigate.

One of the main goals of this design was to get rid of mobile-like interfaces and replace them with native solutions. For example: no navigation drawers, no huge circle buttons for video chats etc.

Another thing to look at is search - one contextual search for entire app, that can be switched to global search at any given moment with ease.

Both - horizontal and vertical folders are enhanced, vertical ones also contain direct buttons to calls and contacts since often there will be more than enough space for it. Horizontal folders have little badge on the side notifying that there's unread folder somewhere out of view, suggesting user to scroll, which can be an issue now in current Unigram.