0 A.D. is a free and open-source real-time strategy video game under development by Wildfire Games. It is a historical war and economy game focusing on the years between 500 BC and 1 BC, with the years between 1 AD and 500 AD planned to be developed in the future. The game is cross-platform, playable on Windows, macOS, Linux, FreeBSD, and OpenBSD. It is composed entirely of free software and free media, using the GNU GPLv2 (or later) license for the game engine source code, and the CC BY-SA license for the game art and music. Gameplay 0 A.D. features the traditional real-time strategy gameplay components of building a base, developing an economy, training an army, engaging in combat, and researching new technologies. The game includes multiple units and buildings specific to each civilization as well as both land and naval units. During the game, the player advances from "village phase", to "town phase", to "city phase". The phases represent the sizes of settlements in history, and every phase unlocks new units, buildings, and technologies. Multiplayer functionality is implemented using peer-to-peer networking, without a central server. Development 0 A.D. originally began in 2001 as a comprehensive total conversion mod concept for Age of Empires II: The Age of Kings. The development team later decided that making the project as a mod was too limiting to their creative freedom, and elected to move their art and ideas to an in-house engine, making it a standalone game. The historical accuracy of the game elements has been the highest development priority. Unit and building names are shown in the original language of the civilization they belong to, and they are also translated into the language in which the user is playing the game. There is also a strong focus on attempting to provide a high visual accuracy of unit armor, weapons, and buildings. On 10 July 2009, Wildfire Games released the source code for 0 A.D. under the GNU GPLv2 (or later) license, and made the artwork available under the CC BY-SA license. There were around ten to fifteen people working on 0 A.D. around 23 March 2010; but since development started, over 100 people have contributed to the project. On 5 September 2013, an Indiegogo crowdfunding campaign was started with a goal. They raised a total of to be used to hire a programmer. The majority of the project's finances are managed