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Gee!Grapple is a Mutator for Unreal Tournament 2003 that gives all players a grappling hook so they can reach high places and fly about with (some) ease.
This may or may not work in UT2004, I haven't tested it because I don't own the game. If anyone tries it out let me know.
Grapple received honorable mention (scroll down to the August 7th entry) in the mutator category for the first phase of the $1,000,000 Make Something Unreal Contest. Thanks!
Here's a couple of screenshots of the Grapple in action:
download the latest version (Version 100, 4/18/03) of the UMOD file
download the latest version (Version 100, 4/18/03) of the source in a zip
For more information check out the Unreal Wiki project page.