Back in the mid and late 90's, a lot of the first person shooter games had these "aftermarket" add-on's sitting near them on the shelf. I remember Duke Nukem typically had the most, but Doom, Shadow Warrior, Redneck Rampage, Sin, Blood, they all had one or two you could find at a Media Play, Best Buy, Circuit City, Target, bunch of places that aren't around anymore. They all said "ADD-ON LEVELS" on them, but very few of them were playable as any kind of single-player campaign, which is probably what many people bought the things for hoping to get (I know I did a couple times). Almost always, they were just custom made multiplayer maps that were ganked off the web (sometimes without permission I think) and piled into a collection on a CD and sold for profit. (Like the back cover says, all the maps are "freeware" public domain, and yet you're still paying them real money for it, ) Many of the maps were just plain old BAD. On the whole, they were usually a waste of money. The REAL add-on's were typically official expansion add-on packs, like Ground Zero and Reckoning for Q2, Suckin' Grits on Rt. 66 for Redneck Rampage, things that were licensed and/or designed by the original studios that made the game.This looks like something I probably saw on a store shelf back in the day. The back cover briefly mentions adding new weapons and monsters... perhaps using whatever front end thing is pictured there (which probably no longer works on modern versions of Windows), but I highly highly doubt there are any actual player single player or coop maps, it's likely ALL multiplayer maps. The "new monsters" part is probably something the front-end does to load a different model in place of a stock one.If they want money for that, I'd recommend not buying it... unless it's a physical copy in great condition with all the original packaging and you're just doing it to "collect" as a fan of Quake2.