UTCP - Unreal Tournament Control Panel
Small control panel which allows the selection of various graphics and sound driver settings which would otherwise need to be manually edited in the .ini file. The latest version includes features for hardware detection.
NB this utility has ceased active development

XQF - Server Browser
A nice front-end for QStat, a server browser for Linux. The latest version of XQF includes support for Unreal Tournament.
Avatar has submitted this patch for version 0.94 of XQF which enables it to launch Unreal Tournament.

The Linux Server Admin Page
Excellent site of resources for admins running UT servers.

Advanced Server Startup script
This is an advanced script for running a UT server on Linux, with features including: start and stop, email notification of crashes, random start map, log backups and compression.
View the changelog for version 102.

Linux UT428a server install package
Enhanced server installation for Linux UT server admins, with working ngWorlStats and various improved default games settings. This is a standalone "dedicated" server package.

Da Kine Linux Server Tool
GUI tool for launching a UT server on Linux. Requires Perl/Tk.

Masquerading firewall settings
ipfwadm/ipchains settings to allow a Linux UT server to run behind a firewall.

ngWorldStats fix
Page with instructions and a script to fix the logging of ngWorldStats for Linux servers.

AEstats
Alternative log stats analyser, which works with numerous 3D shooters including UT.

UTMaps
Cool CGI script to allow users to rank the maps running on a server.
Requires Perl, plus MySQL for full voting functionality.

NOP
Another alternative stats logging package which runs on Linux.

UModPack
Cross-platform utility for decompressing UT modpacks. A must for all Linux players, it features both command-line and graphical interfaces. Recommended.

UT UDP Proxy utility
A UDP proxy program designed to enable LAN-connected clients to play UT over the Internet, over a shared dial-up connection.

UMR - Unreal Media Ripper
This is a utility to rip music and sounds out of Unreal and Unreal Tournament data files.
Download and apply this patch to enable UMR 0.3 to build on non-AMD processors.
NB the authors are seeking further help developing the project, so get involved!