Aftermath:Source

Aftermath is a hl2 mod which involves the player killing waves of the undead with your friends or alone using weapons, your knife or even blow them up with grenades and set them alight with Molotov’s.

Aftermath is point based and requires you to buy weapons and doors with points gained from killing zombies, new features include barriers which allow you to slow down zombies by blocking their path, zombie dismemberment, weapon upgrading, combo bonuses and more maps.