Valve Hammer Editor - Combine OverWiki, the original Half-Life wiki and Portal wiki
I was using the hammer editor and noticed that ragdolls eyes stare at you all the time and its so creepy i kinda wanna stop messing with this map for now :
Hammer Editor image - Source - IndieDB
WIP Map Level Building Using the Hammer Editor by lRezz on DeviantArt
Strange map leak (prop_static) : r/hammer
Valve Hammer Editor - Valve Developer Community
J.A.C.K. :: Official Website
HammUEr, a Hammer/Worldcraft map importer for Unreal Engine - Marketplace - Epic Developer Community Forums
J.A.C.K. on Steam
Valve Hammer Editor 3.5.3 file - ModDB
Steam Community :: Guide :: Hammer Editor - Getting Started and Setting Up
How to Optimize a Map in Hammer Editor: 10 Steps (with Pictures)
Valve Hammer Editor - Official TF2 Wiki | Official Team Fortress Wiki