Ancestry.com is giving free access to 1 billion new records from 67 countries until September 1 (midnight).
Obtain access through the special portal (you may need to scroll down to see it) on the main Ancestry.com page when you are not signed in.
From the map below the special portal search engine, you can see which 43 new countries have been added (orange) and what other countries have newly added databases (green.) From what we can figure out, it is these databases that are included in the free access.
Unfortunately, I have not found a list of which specific databases make up this group.
Good Luck Searching!