War of Attrition is a mod for Duke Nukem 3D.
"In the War of Attrition mod, all 12 of Duke’s weapons gain experience points and upgrade as he uses them. Duke’s max health, armor, and some of his inventory items can also be upgraded. As you progress through the game, you will encounter more powerful monsters to match your increased firepower. Based on the popular Duke Plus mod, Attrition incorporates many of the same features (including advanced monster AI, bot allies, mirrored levels, damage effects, and more). Attrition comes with a large number of high quality fan made levels that have been organized into several episodes. In some of those episodes, missions are selected at random, and you must complete a large number of them finish the game. Addictive with lots of replay value, Attrition showcases some of the best levels ever made for Duke 3D, adding new gameplay but keeping the essence of the original game intact."