PMC Rattler v2.0 for ArmA 3.
This is 25km x 25km desert terrain for ArmA 3, includes airbase, airstrip, war torn cities, villages, dirt road network, harbors and oilfields.
Screenshots: ArmA 2 screenshots page.
--- v2.0 - initial arma3 release
Just copy the addon pbo's into directory of your choice and use -mod parameter to launch ArmA 3. For more details read How to install ArmA 2 Mod.
Download links from PMC Tactical ArmA 3 Downloads page.