A package with a shapes patch, a sounds patch, and a physics model to give you the chainsaw from Doom. Not having ever played Doom (yes, I admit it), I can't say how faithful the reproduction is, but it looks and works pretty well. Also comes with an application patcher, to give you the proper name when you're using the weapon, but I couldn't find a version it worked for (I tried 1.2 and 1.5). If you really care, you can patch your app manually.