Counter-⁠Strike

The Half-Life mod made by Le and Cliffe changed one rule of the shooter, and everything else changed because of it. A killed player doesn't respawn: they wait for the end of the round and watch those still alive. So people play carefully, and every life has a real price: the loss of a player stays with the team until the end of the round. A firefight turns into reconnaissance with rare, short clashes.

Money puts on the same pressure. Equipment is bought at the start of a round with a sum awarded for the results of the previous ones, so a lost round hurts the next one too, and a losing streak forces the team into cheap weapons. You have to count not only positions but also the budget, and skipping a purchase to save up becomes a tactical move. Shooting is built so that accuracy drops while running and jumping, so people fire standing still and in short bursts, and skill here consists largely of restraint. The sides solve different tasks on the same map: plant the explosives or free the hostages. The game came out as free beta versions, and later Valve released it on its own.