The ability to split code and run it concurrently was the holy grail for Flash game developers. Now we can use Actionscript Workers to run code from external SWF files concurrently. With this beta test Adobe will hammer the last problems/bugs and within the next months it will release all that sweetness to everyone.
This new version brings even more to the table. You can use compressed texture with alpha support,
Camera.copyToByteArray/Camera.copyToVector, LZMA runtime compression/decompression on
ByteArray, AIR iOS Push Notifications and AIR direct deployment (without iTunes).
You can check the complete description of each feature here.