There is only one file type that uses the .W3X extension:
Warcraft 3 Expansion Map FIle
A W3X file is a game map or scenario created for Warcraft III: The Frozen Throne expansion pack. It contains terrain information, regions, units, and other objects that can be placed within the map. W3X files may be included with the game or created by players using the Warcraft III World Editor.
W3X files are popularly used for the Defense of the Ancients (DotA) Allstars modification, which is a custom map that has been calibrated for competitive gameplay using custom heroes.
NOTE: Standard Warcraft III maps use the .W3M extension.
Updated: September 21, 2017