Zombie Panic! (ZP) was an old prototype cooperative survival-horror Half-Life 1 modification, first released back on Oct 31, 2004 via ModDB as a beta, and now re-released officially on Steam for free!Following the classic human vs. zombie concept, the game pits a group of survivors against the walking dead. Your goal is to complete a number of objectives to reach safety, or take out the remaining zombies still lingering in the area. But those who were once your friends after death become the very same creatures you're trying to escape.Ammo is a scarce resource, so don't run around guns blazing, or you'll run out of ammo fast and be easy prey. The more weapons and ammo you carry, the slower you move, so sharing what you don't need with your teammates increases your chance of survival.The Steam version features:Half-Life's 25th anniversary supportSteam Achievements and WorkshopNew fatigue system, replacing the 'jump delay'New Zombie vision and ammobank HUD inventoryNew first-person and third-peson animationsNew player models and weaponsNew mapping entities-toolsUpdated User InterfaceUpdated classic maps visuals and gameplayRewritten source code using 'BugfixedHL' as a baseAnd much more!We've also uploaded the source code to GitHub, making ZP1 'source available'!All credits to the original Zombie Panic! team who initially made this prototype in 2004.