Name Of Game: Planetside 2
Genre: First Person Shooter, Massive Multiplayer Online
Information Page: https://www.planetside2.com/
Download Link: https://www.planetside2.com/
Other: Upwards of 1000-man battles(Not exaggerating, each server has three continents, each continent can support up to 2000 players at once)
Not just infantry, there's aircraft and ground vehicles too. A bit pay-to-win, but still fun. No idea how this game is free.