HLMV is a modification of Mete Ciragan's original Half-Life model viewer. It adds support for transparent and additive model textures, weapon origin view, better texture information and a whole bunch of other useful features.
The program is a complete hack as I'm no C++ expert and it was the first C++ program I ever attempted, but here's the list of current enhancements to the default 1.25 viewer:
* GUI re-organised * Default background colour is now blue/grey instead of black * "Save Options" allows you to save your preferences so they are loaded next time you start HLMV * Dump Model Info option creates a text file giving a detailed breakdown of your models internal structure * Acts as a front-end to STUDIOMDL and MDLDEC allowing you to decompile and compile models from within HLMV * Can open GCF, PAK, WAD and BSP files * Poly counter shows how many polygons are being drawn * Supports the Alpha and Additive texture flags * Displays transparent and additive textures in the model preview * Texture flags can be set and previewed and saved to the model * Option to view the UV Map for any given texture * Sequence panel now shows additional sequence parameters * Events for a given sequence can be viewed * Previewing of new weapon origins for v_model's (tweaked this version) * Addition of crosshair and guides for helping with re-origining weapons * Small bugs from HLMV 1.25 fixed