Includes 32- and 64-bit builds, so you can get more power if you're running a modern system.

Vluzacn's ZHLT v34 - The most up-to-date and feature rich version of the Half-Life compile tools, with a host of lighting options and optimization entities.

Often the FGD is included in the mod install folder.

For non-Valve games and mods, consult the mod website.

Sven Co-op: Check your Steam installation, the FGD is included at /Steam/steamapps/common/Sven Co-op/svencoop/sven-coop.fgd.

Counter-Strike: Condition Zero Deleted Scenes FGD.

Goldsource Games FGD Collection - All official Valve games in one convenient file, including Half-Life, Counter-Strike, Opposing Force, etc.

In order to use an editor for more than empty rooms, you'll need a FGD! An FGD file contains the definitions of the entities in a game/mod so you can create a map for it. Unfinished and rather unstable - use with caution.

Sledge Editor - A free, open-source replacement for the Hammer Editor that's no longer being actively developed.

GtkRadiant 1.4 or 1.5 - Half-Life has never been a big focus of the GtkRadiant project, and support for it has been removed in version 1.6.

Don't forget to install the required addons to enable mapping for your chosen HL mod.

Quark - The Quake Army Knife, another tool aimed at being a universal editor.

TrenchBroom has an excellent manual to assist with that, however. A very stable application that is being updated often, but is very different to Hammer, which will make most tutorials difficult to follow. Doesn't currently render sprites and models in the editor, but otherwise fully works for Half-Life mapping.

TrenchBroom - A Quake editor that has support for Half-Life as well.

JACK is almost identical to Hammer, making it easy to use as a drop-in replacement, and tutorials for Hammer will make sense when using JACK. There's a paid Steam version that's slightly more up-to-date, and has Mac support.

Currently the most stable of the modern Hammer clones. The free version runs on Windows and Linux. General-purpose BSP tool aimed at all Quake-based engines.

Valve Hammer Editor 3.5 - The final version of the original, official Goldsrc editor, including model support.

How to edit gmod maps in hammer