There is a long list of supposed features leaked with regards to the upcoming platform:

-  The User Interface is based upon codename 'METRO'. It will be very similar to the Zune HD User Interface with a complete revamp of the 'Start' screen. The UI is 'Very Clean', 'Soulful' and 'Alive'
-  Unfortunately there will be no Flash support at the get go as there was not enough time to implement these features.
-  Windows Phone 7 will only support application installation through service based delivery. (i.e Marketplace). Application installation via storage card will not be possible.
-  No Multi-Task support. Applications will “Pause” when in the background, however will support notifications via push notifications.
-  Marketplace will now support “try before you buy” as well as an API
-  No NETCF backwards compatibility. This means the original rumor of no backward compatibility for applications holds to be true. That being said, there are high hopes of porting the NetCF to the newer platform easily.
-  Microsoft is confident that devices will be ready by September 2010
-  Full Zune Integration
-  Windows Mobile Device Center will no longer be used. Zune software to take over syncing via PC.
-  OEM Interfaces will not be allowed to run on the device. Say goodbye to Sense UI / SPB Mobile Shell / Point UI / Infinity, etc, etc
-  Full XBOX Gaming Integration (Gamer tag, achievements, friends, avatars, merchandising, etc)
-  Full support for social networking