I decided to check the Zynga platform because I heard that Zynga can now host games and one is able to play these games using a Zynga account.
After registering for a game, I noticed that it opened directly and didn't ask me to create an account (as it is using my Zynga account).
The weird thing is the game's website sends you to its facebook page, where I have to log in using my facebook account to play.
How could a facebook game allow someone to play through the Zynga platform?