COD4 Survival Mode Prototype is an experimental mode for Call of Duty 4 Singleplayer that aims to simulate Modern Warfare 3 Survival Mode mechanics on Call of Duty 4. The initial purpose of the mod is to create a basic Survival mode like MW3 with Call of Duty 4 assets in Singleplayer. This means that in the first version of the mode, it will only have weapons, equipment and support items that are available in Call of Duty 4 singleplayer.
This video shows how the gameplay of the mode will more or less be when it is completed. It is showing the similarities and differences that it has with MW3 and it's giving a clear idea of what the mode will be like.