Valve Hammer Editor is a tool that allows the creation of maps for Half Life 2 and Counter-Strike games.
The tool allows you to create maps from blocks, allowing the creation of the entire scenario of the game, including the insertion of objects in it.
In addition, it has several features such as 3D rendering and visualization, animation sequence, among many others.
Don't think twice, and download this tool now, it's completely free and depending on you, you can create incredible maps.