Zombie Panic! is a multiplayer Half-Life modification, developed by the Zombie Panic! Team. Zombie Panic! (Half-Life Modification) is the prototype that eventually became Zombie Panic! Source in 2007.

After roughtly 22 years later after v1.0 release, in 2025, Zombie Panic! got updated to Half-Life 25th Anniversary update using a brand new code base, since the original source code was lost. The source code is also available on Github which you can grab here.