Though it's not Marathon original it does remind me of many old shooter games such the FurFighters. Thank you for the plugin.
Back when items were strictly 2D sprites, there was little reason to care about their facing angle. We now have plugins that replace items with 3D models, yet in nearly all existing maps all weapons and ammo face the same direction.
This plugin addresses this cosmetic oddity by making all items slowly rotate (yaw), as seen in other shooters like Quake and Unreal. The 2D sprites were easy to identify because you could see them in profile from any angle. This animation restores that property, and the movement also makes them stand out more. Unfortunately, because the script physically manipulates the items in the environment, it's only expected to work in single player.
I've been using this for myself ever since thedoctor45 released his excellent 3D items plugin in February 2012. However, it's very simple and should work with any 3D items, for any scenario. Anyone making a "3D items" or similar plugin is welcome to bundle this into their work; one look at the lua and you'll see how simple the effect is to create.