[One] nice feature of Marathon Infinity is two additional programs that come with it: Anvil and Forge. Anvil allows you to modify the weapons and monsters, changing their powers, sounds and looks. It is far easier to change the powers of the monsters than it is to add original graphics. Forge is a wonderful map design program. Simply draw a two-dimensional map, add floor and ceiling heights and jump into the three-dimensional space. Then run around splashing color on the walls and floor.