Files with ATLAS extension are associated with Stronghold 3, a computer game developed by Firefly Studios. ATLAS files store information related to game maps and can be edited using official map editor available in-game.

Stronghold 3 is a real-time strategy game based around building castles. ATLAS files allow users to add new maps to the game or modify the existing ones by adding, for examples, new buildings. Stronghold 3 was released in 2011, but wasn’t received well gamers and was heavily criticized by reviewers.