Hammer Editor is a level design tool used primarily for creating maps for video games, particularly those built on the Source engine. It allows designers to construct 3D environments by placing objects, textures, and lighting, enabling them to visualize and manipulate game spaces effectively. The editor features a user-friendly interface with multiple views, including 2D and 3D perspectives. Users can create complex structures, set up gameplay elements, and test their designs within the game. Hammer Editor is widely used in the gaming community, especially for popular titles like Half-Life 2 and Counter-Strike.