One of the exciting new features in Halo 3 is Forge. Forge is not a typical map editor like the one you see in many other games. It does not allow you to change anything important in the level, such as the geometry of the level. Rather, it allows you to place weapons, items, vehicles, spawn points, or Halo 3 tools. For example, you can easily place a flamethrower and bubble shield on your base for your teammates to collect. You have a lot of flexibility in what you can place, but you are limited by the number of objects you can place; there is a cost associated with each item. You have a maximum dollar amount that you can spend to avoid memory overflow. Small items cost less, while larger items, such as vehicles, cost more.
You can also play Forge with friends, allowing you to eliminate enemy items while placing items for your own team. Up to seven of your friends can join you by forming different teams. They can attack each other and go into edit mode, making them a monitor like Guilty Spark. You can be attacked while in this mode, so you have to pay attention to your enemies, but you can drop or move any object you want. It has some limitations, like not being able to remove vehicles when there are still people in them.
The Forge seems like a great addition to the Halo franchise that should have many unique gaming experiences in our multiplayer games.