The MelPyth mod is a mod for AvP Gold Edition. Around 2004, modders Melanikus and Python (aka astro_muppet) collaborated on an extensive update to AvP Gold Edition. This includes several new features, such as the shotgun, shoulderlamp, and multiplayer commands like kicking players, locking servers, and viewing player tags. It was publicly released in 2005 as M4, aka version 1.0. However, a much more extensive version was also made, which was called M5, aka version 1.1. This version added many new features to M4, including such additions as a sniper rifle, a revolver, M79 grenade launcher, a mech with machine guns and flamethrowers, support for textures above 128x128 pixels, and a third-person perspective. Melanikus was generous enough to allow me to share it with you all. While M5 is less stable than M4 and technically an unfinished project, it is the most extensive AvP Gold mod that remains completely faithful to the original game. Created by Melanikus and Python (aka astro_muppet).
Although it is very unfortunate no proper AVP CLASSIC 2000 remake of this was ever made, I managed to get working nonetheless with my Steam copy, and even so on Linux.
It's an ancient yet a magnificant mod for rediscovering the single player campaign, although its multiplayer features are completely obsolete as AVP CLASSIC 2000 now has MP through Steam (and uMod obviously works better for MP enhancement)