Comments - Zockerfreak112

You are right, the mod has no .exe. It can be started by starting Half-Life as normal, clicking on "Change game" and chosing Decay (the name depends on the name of the Decay-containing folder inside the Half-Life main folder).

I'm not sure, but having the Steam version of Half-Life makes the mod also startable in the Steam library. But the WON version has to be started with the "Change game" method explained above.

You have to copy the "decay" folder into the in the "...\common\Half-Life" folder. If it's the WON and not the Steam version, it also has to be in the Half-Life folder.
The game can be started by starting Half-Life, clicking on "Change Game" in the main menu and chosing "Decay".