Half-Life Asset Manager is a modeling tool based on Half-Life Model Viewer 2. Incorporating many improvements, this is the best model viewer for Half-Life 1. Note: this tool only supports Half-Life 1/GoldSource, not Half-Life 2/Source and Source 2!
Full changelog: Github.com
Minimum requirements: Windows 7, a graphics card capable of using OpenGL 2.1 or newer
Website: Github.com
If your computer does not meet the minimum requirements, Half-Life Model Viewer 2.11 is an older version of Half-Life Asset Manager that works on Windows XP: Moddb.com
Nice.