Epoch Mod - http://www.epochmod.com
Arma 3: Epoch Mod is currently licensed under:

Epoch Mod by Epoch Mod Team is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. 
http://creativecommons.org/licenses/by-nc-nd/4.0/

You must also abide by all license and game usage restrictions from BI: 
Arma 3: End User License: https://www.bistudio.com/community/licenses/arma3-end-user-license
Arma 3: Game Content Rules: https://www.bistudio.com/community/game-content-usage-rules