Battle.net

Battle.net is Activision-Blizzard's proprietary store and game launcher platform on PC. It was originally the only platform that Destiny 2 was sold on, on PC. The game was sold there from launch in 2017 until the release of Shadowkeep in 2019 when it was removed, in favour of Steam. The switch was made due to Bungie becoming the sole publisher of the game and cutting ties with Activsion.