Another event invite has been sent out today, but this time it's not from Microsoft. Facebook has sent out invites for a mystery event being held at their headquarters in Palo Alto at 10am PT/1pm ET. There's not a single hint on the invitation, and speculation has only been limited to a phone recently, even though Facebook denied it. What could this be? We're two short days away to finding out. Whatever it is, it's probably going to be big.