Age of Empires II: Forgotten Empires is now available for download over here! It's an unofficial expansion pack that requires Age of Empires II as well as the Age of Empires II: The Conquerors expansion.
The fan-made expansion introduces five brand new civilizations (Italians, Indians, Slavs, Magyars, and Incas), 30 new technologies, nine new units, 11 new maps a new campaign, a new building, two new architecture sets, and 20 new scenario editor objects. Support for widescreen resolutions of up to 1920*1440 is also included.
It's still a work in progress though, more campaigns will be added at a later date.