Aleph One, the open-source version of the Marathon 2 engine, has many new features, among which is a scripting language that allows scripters to modify many things related to gameplay. These Lua scripts come in many forms, but the best so far is this: a replacement script for Aleph One's built-in Capture the Flag game type. It's fun. You'll only need the script if you plan on hosting. Download the file and look at the Readme to find out more.