Hammertime

Hammertime is an open-source Fork of Sledge which is an open-source Alternative to Valve's Hammer Editor for the Goldsource engine. It is written in .NET and uses Veldrid for rendering, with DirectX 10.

Hammertime supports Goldsource mapping, and is constantly being updated to add more Features, some of these Features include:

• Prefabs!
• Lighting Preview inside the Editor (Just like Hammer++!)
• Other various improvements!

Here are also some good Community Editors if you need some:

• TrenchBroom: TrenchBroom is a free (GPLv3+), cross platform level editor for Quake-engine based games. It supports Quake, Quake 2, Hexen 2 and Half-Life
• Valve Hammer Editor: Found in the steam Library under HL1 SDK
• JACK: J.A.C.K is a Version of Hammer / Worldcraft that introduces lots of new features and improvements.

The Hammertime Editor is licensed under BSD-3.