To install on Mac go to your /Library/Application Support folder. In there, find the Marathon game folder (or Aleph One folder if you're using a third-party scenario) of the game you wish to install this script in and place it in it's "Scripts" sub-folder.
You can also install it on all user accounts by embedding it in the Marathon game of your chosing. To do so, right click on the Marathon app (or Aleph One app if you're using a third-party scenario) you want to install it in and select "Show Package Contents". A window will pop up showing you the internal components of the application. Navigate to Contents/Resources/DataFiles/Scripts then place the FOV.mml script in that folder. Note: you will need to repeat this process with each Aleph One/Marathon update as every update overwrites the game's app file.

To install on Windows & Linux simply place it in the "Scripts" folder of your game's executable.


If you you like the script but feel the "fish-eye" effect is too much you can modify the script's number variables (the ones in quotation marks) to adjust it to your liking.
This script will not work on scenarios that have their own FOV modification scripts included.

Special thanks to General Tacticus for showing me this trick in the first place.