JACK and Hammer
What is Hammer 3.4?
Hammer 3.4 is a editor made for Half-Life. It features a grid display system with 4 frames that display: 3D view, Top, Side, and Front. This editor allows you to do a lot of editing.
Why is J.A.C.K. better?
J.A.C.K. is easier to setup up and use. It allows you to view your map's features in real time. You can also listen to sounds you placed on your map. J.A.C.K. is already setup and ready for most of your mods. Just pop in a game data file and a few textures and your ready to go. J.A.C.K. is perfect for Day of Defeat maps.