Duke Nukem: Weapon of Mass Destruction is a gameplay mod for Duke 3D, and it requires EDuke32 (the excellent source port by TerminX) to run. DNWMD can be played with the original episodes as well as most custom maps.
While DNWMD contains virtually no new graphical content as of yet, it features a variety of new and challenging enemies which randomly replace some of the standard ones. It also features an alternate weapon mode for each of Duke’s weapons, as well as a host of other player enhancements, including double jumping and improved inventory items. Chief amongst these is the Dukebot, a companion that replaces the stationary HoloDuke. The Dukebot fights alongside the player and is able to use most of the weapons in Duke’s arsenal, as well as a Street Fighter 2 style hurricane kick when it runs out of ammo (which it knows how to pick up, by the way). An upgrade menu allows Duke to spend skill points (obtained from “soul coins” dropped by enemies) to upgrade himself in various ways, including his max health and weapon damage. In the future, there will be a save/load character feature. While playable, DNWMD is not anywhere near completion.
The modification is regulary updated and released so new features are added and bugs are fixed constantly. You can follow the progress at 3DRealms / AMC. However updated more at AMC. Also on the website is the mod zipped up with Battlefield 3 map by Sang which should be worth checking out.